Monolithically integrated multi-sensor device on a semiconductor substrate and method therefor

ABSTRACT

A monolithically integrated multi-sensor (MIMS) is disclosed. A MIMs integrated circuit comprises a plurality of sensors. For example, the integrated circuit can comprise three or more sensors where each sensor measures a different parameter. The three or more sensors can share one or more layers to form each sensor structure. In one embodiment, the three or more sensors can comprise MEMs sensor structures. Examples of the sensors that can be formed on a MIMs integrated circuit are an inertial sensor, a pressure sensor, a tactile sensor, a humidity sensor, a temperature sensor, a microphone, a force sensor, a load sensor, a magnetic sensor, a flow sensor, a light sensor, an electric field sensor, an electrical impedance sensor, a galvanic skin response sensor, a chemical sensor, a gas sensor, a liquid sensor, a solids sensor, and a biological sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.16/683,469 filed on Nov. 14, 2019 the disclosure of which is herebyincorporated by reference in it's entirety. U.S. application Ser. No.16/683,469 is a continuation of U.S. application Ser. No. 15/893,649filed on 2018 Feb. 11 the disclosure of which is hereby incorporated byreference in it's entirety. Application Ser. No. 15/893,649 is acontinuation of U.S. application Ser. No. 15/049,339 filed on Feb. 22,2016 the disclosure of which is hereby incorporated herein by referencein its entirety. Application Ser. No. 15/049,339 is a continuation ofapplication Ser. No. 14/207,419 (U.S. Pat. No. 9,266,717 Issued Feb. 23,2016), Ser. No. 14/207,433 (U.S. Pat. No. 9,580,302 Issued Feb. 28,2017), Ser. No. 14/207,443 (U.S. Pat. No. 9,327,965 Issued May 3, 2016),and Ser. No. 14/207,461 (U.S. Pat. No. 9,862,594 Issued Jan. 9, 2018)all filed on Mar. 12, 2014, wherein each application listed above ishereby incorporated by reference in its entirety. Applications Ser. Nos.14/207,419, 14/207,433, 14/207,443, and 14/207,461 further claim thepriority benefit of U.S. Provisional Patent Application No. 61/793,860filed on 15 Mar. 2013 the disclosure of which is hereby incorporatedherein by reference in its entirety.

FIELD

The present invention generally relates to sensors and moreparticularly, to different types of sensors formed on single or commonsubstrate.

BACKGROUND

Many devices and systems include various numbers and types of sensors.The varied number and types of sensors are used to perform variousmonitoring and/or control functions. The systems can be active usingreal-time measurement data form the sensors in a work-flow or to controldecision processes in operating devices. Sensors are used in conjunctionwith interface circuitry and control circuitry to interface withdifferent sensor types, to control when measurements are taken, and toactively process the measurement data. Sensors are placed in proximityto the parameter being measured. Sensors can require direct interactionwith the parameter of interest or conversely can be measured indirectly.In general, the number and uses of sensors is growing and being appliedin a number of new and different applications.

Sensors can be mechanical, chemical, biological, electro-mechanical, orsolid state to name but a few. A sensor is a singular component that iscoupled to other electronic circuits via a printed circuit board orother connection means. MEMS (Micro-Electro-Mechanical Systems)technology is a type of micro-fabrication technique used to form asensor that interacts with the environment to measure physical,chemical, or biological parameters. Thus, in recent years, many of thesensors used to perform monitoring and/or control functions use MEMStechnology for their implementation. These sensors provide electricalparameters such as voltage, current, frequency, etc. as inputs to theinterface circuits that are equivalent to the physical, chemical,biological etc. parameters that are being measured. At issue is thatthese sensors and other types of sensors are separate devices or aplurality of devices of the same type or measure similarly. Often toincrease functionality or add further sensing capability differentsensor types are combined in a package or on a PCB. This results in alarger foot-print, higher power consumption, higher complexity,increased cost and more complicated fabrication and assembly processes.Therefore, there is a need and benefit to combine sensors of differenttypes that measure different parameters, in a monolithic process, and ona semiconducting substrate that reduces the size, improves performance,lowers cost, and reduces manufacturing and assembly complexity.Furthermore, this will open the door to new and different applicationsthat were limited by the scale of system integration.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features of the system are set forth with particularity in theappended claims. The embodiments herein, can be understood by referenceto the following description, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1. illustrates example embodiments of Direct Interface Sensors(DIS);

FIG. 2 illustrates an example embodiment of an Indirect Interface Sensor(IIS);

FIG. 3 illustrates an example embodiment of a MIMS device(Monolithically Integrated Multi-Sensor);

FIG. 4 illustrates an example embodiment of a MIMS device(Monolithically Integrated Multi-Sensor) including sensor and fieldregions;

FIG. 5A illustrates a simplified cross section view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 5B illustrates a simplified cross section view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIGS. 6-29) are simplified cross section views of the MIMS device shownin FIG. 5B illustrating the various exemplary methodological steps thatare used to make various MIMS devices in accordance with exampleembodiments;

FIG. 30 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 31 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 32 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 33 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 34 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 35 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 36 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 37 illustrates a simplified cross view of a MIMS device(Monolithically Integrated Multi-Sensor) in accordance with an exampleembodiment;

FIG. 38 illustrates a MIMS device (Monolithically IntegratedMulti-Sensor) in a cellphone in accordance with an example embodiment;

FIG. 39 illustrates a MIMS device (Monolithically IntegratedMulti-Sensor) in a wearable device in accordance with an exampleembodiment; and

FIG. 40 illustrates a MIMS device (Monolithically IntegratedMulti-Sensor) in a transportation device in accordance with an exampleembodiment.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help improve theunderstanding of the embodiments of the present invention.

DETAILED DESCRIPTION

The following description of exemplary embodiment(s) is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the art may not be discussed in detail but areintended to be part of the enabling description where appropriate. Forexample specific computer code may not be listed for achieving each ofthe steps discussed, however one of ordinary skill would be able,without undo experimentation, to write such code given the enablingdisclosure herein. Such code is intended to fall within the scope of atleast one exemplary embodiment.

In all of the examples illustrated and discussed herein, any specificmaterials, such as temperatures, times, energies, and materialproperties for process steps or specific structure implementationsshould be interpreted to be illustrative only and non-limiting.Processes, techniques, apparatus, and materials as known by one ofordinary skill in the art may not be discussed in detail but areintended to be part of an enabling description where appropriate. Itshould also be noted that the word “coupled” used herein implies thatelements may be directly coupled together or may be coupled through oneor more intervening elements.

Additionally, the sizes of structures used in exemplary embodiments arenot limited by any discussion herein (e.g., the sizes of structures canbe macro (centimeter, meter, and larger sizes), micro (micrometer), andnanometer size and smaller).

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed or further defined in the followingfigures.

Modern electronic systems use different sensors that interact with theenvironment and transduce this information into the electrical domain.The input domain thus can be physical, chemical, biological etc. Thus,the sensors that interact with these domains can be classified asphysical, chemical and biological sensors. These sensors may use avariety of transduction principles (based on physical, chemical andbiological phenomena) to produce the equivalent electrical parametersthat are the inputs to the interface circuit.

In order to derive benefits of high performance, low cost, low powerconsumption, small size and form factor, these sensors are realized insingular form by integrated circuit processes. Examples of differentsensors that are useful for providing input to a system are physicalsensors such as:

Inertial sensor—linear acceleration—multi-axis

Inertial sensor—angular acceleration—multi-axis

Inertial sensor—vibration—multi-axis

Inertial sensor—shock—multi-axis

Inertial sensor—angular rate—multi-axis

Pressure sensor—absolute

Pressure sensor—differential

Pressure sensor—gage

Tactile sensor—touch

Humidity sensor—relative humidity

Temperature sensor—ambient

Temperature sensor—infra-red

Temperature sensor—contact

Microphone—audio

Force sensor—force

Load sensor—loads and strain—multi-axis

Magnetic sensor—multi-directional magnetic fields

Flow sensor—fluid flow

Light sensor—imaging

Electrical field sensor

Electrical impedance—probe

Galvanic Skin Response sensor

Chemical sensors:

Various chemicals including gases, liquids and solids

Biological sensors:

Various biological samples of cells, tissue, fluids

Biological probes for neural, muscular signals

The sensors can be classified also by how they interact with themeasuring environment. In a broad classification, sensors can beclassified as Direct Interface Sensors (DIS), Indirect Interface Sensors(IIS), and Direct Interface Sensors.

Some sensors need to interact directly with the sensing environment andmust be exposed to the sensing medium. These sensors are called DirectInterface Sensors (DIS). The DIS must interact directly with themeasurand and be able to withstand all the effects due to the exposureto the media where the sensor is used. Some examples of this class ofsensors are pressure sensors where the ambient pressure must act on themeasuring membrane and then transduced to an equivalent electricalsignal. Similarly, a humidity sensor is exposed to the ambient humidityand provides an equivalent electrical signal. Also, a microphoneresponds to the sound waves and is directly exposed to it. Themicroprobes that are fabricated have to be in contact with thebiological component that it is measuring. A neural probe has to be incontact with nerve cells while a muscle stimulating electrode mustcontact with muscle cells. Similarly, a flow sensor is exposed to theflow of the fluid directly to measure the flow. FIG. 1 illustratesexample embodiments of Direct Interface Sensors.

Direct Interface Sensors can be further classified as:

Direct Interface Sensors—No Line of Sight

Direct Interface Sensors—Line of Sight

Direct Interface Sensors—Through a Medium

Direct Interface Sensors—No Line of Sight

These Direct Interface Sensors need to be directly exposed to thesensing environment and not in the direct line of sight of the parameterthat is being measured. In this case, the sensor responds to the sensedparameter of interest and do not need to be in the direct line of sight.An example of this type of DIS is a pressure sensor that senses theambient pressure and produces a transduced signal. Another example wouldbe a humidity sensor that senses the ambient humidity and produces theequivalent transduced signal. A pressure sensor 100 is a directinterface sensor and a humidity sensor 110 is also a direct interfacesensor.

Direct Interface Sensors—Line of Sight

These Direct Interface Sensors need to be directly exposed to thesensing environment and directly in the line of sight of the parameterthat is being measured. An example would be an optical sensor that isreceiving input from the light source in front of it. Another examplewould be a microphone which is receiving audio energy from an audiosource in front of it. Another example of a direct interface sensorwould be a Galvanic skin Response sensor.

In FIG. 1, 120 is a microphone as an example of direct interface sensorwith line of sight.

Direct Interface Sensors—Through a Medium

These Direct Interface Sensors need to be exposed to the sensingenvironment but not directly but through a medium. These sensors sensethe parameter of interest through a medium. An example of this type ofDIS would be a magnetic field sensor which can be enclosed in a cavityand still be exposed to the parameter of interest and produce anequivalent transduced signal. Another example of this sensor can be anoptical sensor in a cavity with an optically transparent window andwhich produces an equivalent transduced signal.

In FIG. 1, 130 is a magnetic sensor which is enclosed in a cavity tosense the magnetic field and 140 is an optical sensor which is enclosedin a cavity with a transparent window.

Indirect Interface Sensors

The second class of sensors does not need to be in direct contact orhave direct exposure to the measuring environment. In this class ofsensors, the sensing element or elements are indirectly exposed to themeasurand and then provides a transduced electrical signal. This classof sensors is classified as Indirect Interface Sensors (IIS). An examplefor an IIS is an inertial sensor such as an accelerometer where thesensor element is in an enclosed environment and responds to the changein the acceleration and provides an equivalent electrical signal. Inthis class of sensors, the sensor element is not directly exposed to themeasuring environment. Similarly, a gyroscope responds to the rate ofrotational change without being exposed to the measuring environment.FIG. 2 illustrates an example embodiment of an Indirect Interface Sensor(IIS). An accelerometer 200 can be used as an example of an IndirectInterface Sensor.

The design and fabrication of sensors for measuring differentenvironmental parameters have some common characteristics that can beutilized when combining sensors.

These structural elements may contain elements that respond to differentphysical, chemical, biological inputs. These structural elements mayperform mechanical, electrical, chemical, material functions that enablethe functioning of the sensors. The structural elements can be static orcapable of movement, where it responds to an input or is subjected tomovement by application of an applied force. These structural elementscan form different parts of a sensor such as

Suspensions

Plates

Beams

Membranes

Diaphragms

Wires

Anchors

Pillars

Posts

Walls

Tubes

Tips

Cavities

Sealed cavity in vacuum

Sealed cavity under pressure

These structural elements can perform different functions that enablethe implementation of different sensors

Moving electrodes

Reference electrodes

Test electrodes

Shielding electrodes

Platforms for sensing materials

Provide electrical isolation

Provide thermal isolation

Provide mechanical isolation

These structural elements can be implemented in different sensors toprovide different functions for different sensors. By combiningdifferent structural elements to provide different functions fordifferent sensors, multiple sensors can be implemented using a paralleldesign method and common fabrication process. The sensors can becombined using a structured method which is described below

Determine the sensors required for the platform

Define the performance specifications for each sensor

Choose a common transduction principle for the majority of thesensors—capacitive, piezoresistive, piezoelectric, optical, resonant

Determine the transduction principle for the rest of the sensors

Identify the sensor with the highest fabrication complexity

Determine the fabrication flow for the sensor with the highestcomplexity

Determine the structural components for each of the other sensors

Determine the unique requirements for each sensor

Design each sensor for the specified performance

Iterate as needed until all performance specifications are met

By combining different structural components from different sensors, itis possible to integrate multiple sensors on a common substrate thatshare structural layers for their implementation. This may be defined asa MIMS (Monolithically Integrated Multi-Sensor). A MIMS device may bedefined as a collection of multiple sensors that are formed usingsubstantially common layers on a common substrate. These multiplesensors perform different functions and respond to different inputstimulus. The term “Monolithically Integrated” implies implementation onthe same substrate, which may be a wafer. The substrate may be formed ofsemiconducting wafers or on conductive or non-conductive layers. Theterm “Multi-Sensor” means a number of at least two sensors formed on thesubstrate. The sensors formed on the MIMS device may comprise of directinterface sensors and indirect interface sensors. The multiple sensorsof a MIMS device may be formed on a single substrate and then combinedwith an integrated circuit or it can be comprised of multiple sensorsformed on the same substrate as an integrated circuit. Thus, a MIMSdevice may comprise of multiple sensors on the same substrate which maybe semiconducting and also used to form an integrated circuit. Thelayers used for the implementation of a MIMS device may consist of asubstrate on which different materials may be deposited, grown orformed. The substrate may itself be considered as a layer used for theformation of the MIMS device. The substrate may be formed ofsemiconducting material and may comprise of single crystal silicon,germanium, gallium arsenide, gallium nitride, indium phosphide and thelike. The substrate may also comprise of layers of materials that can besemiconducting, insulating and the like. An example of a layeredsubstrate may be a SOI (silicon on insulator) where a semiconductorsilicon wafer is bonded to another semiconductor silicon layer with anintermediate bonding layer of insulating oxide. Another example of alayered substrate may be a SOS (silicon on sapphire) where a siliconsemiconducting layer is boned to the surface of a sapphire insulatingwafer.

The layers used for the MIMS device can also be deposited on the surfaceof the substrate and can be deposited using semiconductor processes suchas LPCVD (Low Pressure Chemical Vapor Deposition), PECVD (PlasmaEnhanced Chemical Vapor Deposition), APCVD (Atmospheric PressureChemical Vapor Deposition), SACVD (Sub Atmospheric Chemical VaporDeposition), PVD (Physical Vapor Deposition), ALD (Atomic LayerDeposition), MOCVD (Metallo-Organic Chemical Vapor Deposition), MBE(Molecular Beam Epitaxy) and the like. The layers of a MIMS device canalso be sputtered, evaporated, spin-coated, spray coated, electro-platedand the like.

The layers used for a MIMS device can also be grown using such processesas thermal growth, such as silicon dioxide, epitaxially growth usingsuch processes as low temperature epitaxial growth, non-selectiveepitaxial growth and the like.

The layers used for a MIMS device are formed on the entire surface ofthe substrate for forming multiple sensors and then patterned to formelements or components of different sensors. The layers used for a MIMSdevice may be patterned using resist and photolithography and thenetched using a wet etch, dry etch, a combination of wet and dry etch.The layers used for a MIMS device may also be patterned using physicalmethods such as laser etching, ion-milling and the like.

The patterning of the layers used in a MIMS device forms differentstructural components for different sensors that can be static ordynamic. The combination of these layers and the components formed usingpatterning allows for multiple sensors to be formed on a commonsubstrate for a MIMS device. The multiple sensors formed on a MIMSdevice may consist of Direct Interface Sensors, Indirect InterfaceSensors and a combination of the two.

The MIMS device may consist of an integrated circuit formed on the samesemiconducting substrate or it may be combined with the integratedcircuit using wirebonding or stacking or a combination of the two. For aMIMS device stacked with an integrated circuit, the MIMS device and theintegrated circuit are placed so that electrical contacts from the MIMSdevice are vertically connected to the corresponding electrical contactsof the integrated circuit. The vertical contacts between the stackedMIMS device and integrated circuit may use vertical interconnects suchas TSV (Through Silicon Vias), flip-chip, and the like. The verticalinterconnects may use a bond or solder to reduce contact resistancebetween the electrical contacts of the MIMS device and the interfacecircuit.

FIG. 3 illustrates a MIMS device 300 formed on the same substrate 320and containing a Direct Interface Sensor 325 and an Indirect InterfaceSensor 330. Another example of a MIMS device 350 is shown in FIG. 3where the same common substrate 340 is used to form Indirect InterfaceSensor 355, a Direct Interface Sensor 360, a Direct Interface Sensorwith line of sight 365 and a Direct Interface Sensor inside a cavity370.

An exemplary description of a MIMS device with multiple sensors formedon a common substrate is described. FIG. 4 illustrates an exampleembodiment of a MIMS device (Monolithically Integrated Multi-Sensor)including sensor and field regions. A device 400 is shown having asubstrate on which multiple sensors are formed. In the exemplarydescription, three sensors are shown that are formed on a commonsubstrate. The substrate 450 is the initial surface on which the sensors402, 402, 404 are formed. Each sensor formed on the substrate has afield region and a sensor region. Thus, sensor 402 has field region 407,and sensor region 408, sensor 404 has field region 409, sensor region410 and field region 411 and sensor 406 has sensor region 412 and fieldregion 413.

The substrate 450 is the initial surface on which the sensors areformed. The substrate 450 may also be used for forming other devicessuch as semiconductor devices, integrated circuits, actuators. Thesubstrate 450 may be in the form of wafers that are typically round inshape. It may also be of other shapes such as squares, rectangles thatmay be compatible with semiconductor fabrication process. If substrate450 is in the form of wafers, it may be formed with single crystalsilicon. Substrate 450 may also be formed with multiple layers thatcontain both conducting and insulating layers. In one embodiment, it maybe composed of silicon on insulator (SOI). In other embodiments, it canbe SOx, (silicon on x—where x is a carrier wafer that may be composed ofgermanium, sapphire, silicon carbide). For the embodiment where thesubstrate is SOI, it consists of a carrier wafer formed on singlecrystal silicon known as the handle wafer. Above the handle wafer is anintermediate layer of silicon dioxide known as the Buried Oxide (BOX).Above the BOX, there is another layer of single crystal silicon layercalled the device layer. The substrate may also be used for theimplementation of the different sensors.

The field region for each sensor contains elements that enable thesensor to be connected to an integrated circuit that converts thesignals from the sensors into equivalent electrical signals. Theseelements can be interconnects that connect to the various electrodes ofthe sensor to other connection elements that connect to the interfacecircuit. The interface connecting elements can be bondpads, contactbumps, vertical interconnects, planar interconnects among others. If theconnection elements are bondpads, wirebonds are formed that electricallyconnect each electrode to a corresponding bondpad in the interfacecircuit. If the connection elements are contact bumps, the electrode ofthe sensor is connected to a corresponding contact bump of theintegrated circuit using a flip-chip assembly. If the connectionelements are vertical interconnects, each electrode of the sensor isconnected through the substrate in which the sensor is formed to acorresponding electrode of the integrated circuit using an intermediateconnection conductive layer. If the vertical interconnects are formed ina silicon substrate, they are called through silicon vias (TSV). If thesensor is formed monolithically with the integrated circuit, eachelectrode of the sensor is connected to the corresponding electrode ofthe integrated circuit using planar interconnects.

In addition to the interconnects that connect to each electrode of thesensor, the field region may also contain electrodes that provide otherfunctions such as shielding from electro-magnetic fields. Theseshielding electrodes can be formed for each interconnectstructure—wirebonds, contact bumps, vertical interconnects. Theseshielding electrodes can be connected to different electrical potentialsto protect the sensor electrodes from electromagnetic fields.

The sensor region for each sensor contains elements that are utilized inthe design and functioning of the sensor. These elements form thestructural components of each sensor to provide the specific functionfor which the sensor is designed. These structural components performdifferent functions which together enable the sensor to perform thefunction for which it is designed. These structural components orelements may be static, in which case, they do not move relative to thesubstrate on which the sensor is formed. Other structural elements orcomponents may be dynamic, in which case, they may be capable ofmovement relative to the substrate on which the sensor is formed. Themovement that the dynamic structural components perform may be linear,angular, rotational or a combination of motions. The linear motion maybe on 1, 2 or 3 axis. The angular motion may also be in 1, 2 or 3 axis.The rotational motion may also be in 1, 2 or 3 axis (roll, pitch andyaw).

The static and dynamic structural elements or components in the sensorregion are connected to the interconnects in the field region. Thestatic and dynamic structural components are thereby connected to theinterface circuit.

The static and dynamic structural elements or components are formedusing different structural layers. These structural layers are formed byusing different materials used in the formation of semiconductor andsensor fabrication process. These layers can be conductive, insulating,semiconducting among others. These layers can be formed using differentsemiconductor processes such as thermal oxidation, epitaxy, LPCVD (LowPressure Chemical Vapor Deposition, PECVD, APCVD, SACVD, Sputtering,evaporation. Other techniques may include spin-on glass, spraydeposition etc. Some of the commonly used structural layers are

Single Crystal Silicon

Silicon/Germanium

Silicon dioxide

Polycrystalline silicon

Polycrystalline Germanium

Silicon nitride

Silicon oxynitride

Silicon Carbide

PSG (phospho-silicate glass)

BPSG (borophosphosilicate glass)

Metals

Polyimide

Parylene

Pyrex glass

The static and dynamic structural components or elements are formedusing the different structural layers used for the fabrication of thesensor. Each sensor is designed and fabricated using static and dynamicstructural components that are formed using the different structurallayers.

Different sensors can be formed on the same substrate using the same setof structural layers. The same structural layer in one sensor may beused for forming different structural components to perform one functionwhile the same structural layer may be used for forming another set ofstructural components in another sensor. For example, a structural layerused for forming a static component in one sensor may be used forforming a dynamic component in another sensor. Another example is astructural layer that is used to form a structural component that isinside a sealed cavity in one sensor may be used for forming anothercomponent in another sensor that is exposed to the ambient environment.It is obvious to one experienced in the art that a single structurallayer may be used for different structural components in differentsensors formed on the same substrate. This ability to use the samestructural layer for forming static and dynamic components for formingdifferent sensors enables flexibility in design of multiple sensors onthe same substrate.

The choice of structural layers can have a profound effect on theperformance of the sensors that can be designed using a co-design orparallel method. By using the principles of structured design, multiplesensors can be designed using the common fabrication process thatsatisfies the performance specification for each sensor.

The substrate may also be used for forming structural components ofdifferent sensors formed on its surface. Both the top surface and bottomsurface may be used for forming structural components of differentsensors. The substrate can also be used as a structural layer for theformation of different sensors. If the substrate is composed of a SOI(silicon on insulator) wafer, all the three layers—handle wafer, buriedoxide and active or device layer can be used as structural layers forformation of different structural components for different sensors.Thus, static and dynamic components of different sensors can be formedusing the handle wafer, buried oxide and active or device layer. Forexample, in one sensor, the handle wafer may be used for forming adynamic structural component, while in another sensor, the handle wafermay be used for forming a static structural element. In another example,the buried oxide may be partially removed in the sensor area for onesensor, while in another sensor, the buried oxide may be used for astatic structural element. In yet another example, the active or devicelayer may be used to form a dynamic structural element for one sensorwhile the same active or device layer may be used for a staticstructural component for another sensor.

Turning now to the description, and with reference first to FIG. 5A, asimplified cross-sectional view of an exemplary MIMS device 500 isdepicted. The device 500 consists of three separate sensors that aresubstantially formed simultaneously. The depicted device 500, which isshown in simplified cross-section form, comprises an inertial sensor502, such as an accelerometer, a pressure sensor 504, and a soundsensitive microphone 506.

The exemplary device 500 is formed on an SOI (silicon on insulator)wafer 516. The SOI wafer 516, as it is generally known, includes ahandle layer 519, an active layer or device layer 517 and a sacrificiallayer 518 (known as the BOX—buried oxide layer) disposed between theactive layer 517 and the handle layer 519.

The sensor region and the field region are both formed in the activelayer 517. The sensor region in the active layer is where the sensor isformed and the field region is a region of the active layer that remainsin contact with the handle layer, via the sacrificial layer 518. In thisexemplary device, the sensor layer is completely or partially releasedfrom the handle layer 519. The device 500, in this exemplary embodiment,may contain multiple field regions, 507, 509, 510, 512, 513 and 515. Thedevice 500, in this exemplary embodiment, may contain multiple sensorregions, 508, 511 and 514, where the accelerometer 502, pressure sensor504 and microphone 506 are formed. The field regions 507, 509, 510, 512,513 and 515 in the device 500, in this exemplary embodiment, may containstructures to transfer leads from the sensor regions to the handle layerusing through vertical interconnects or silicon vias (TSV) 650, 651,652,653, 654, 655 and 656 as shown in FIG. 5B. The TSVs transfer theelectrical connections from the sensors to an integrated circuit usingbonding technology.

The structural layers used in this exemplary embodiment are used forimplementing different structural components for each sensor. For thisexemplary embodiment, each structural layer is used in theaccelerometer, pressure sensor and microphone for implementing differentstructural components that can be static or dynamic. In this exemplaryimplementation, there are other structural layers which are removed inintermediate steps in the fabrication process. These structural layersmay be partially or completely removed from the sensor region for eachsensor.

In this exemplary embodiment of a MIMS device, the structural layersthat are used for the co-design and parallel fabrication contains layersthat have different material, mechanical, electrical properties that cancombined for the implementation of the different sensors as illustratedin a simplified cross-sectional view of FIG. 5 b.

The handle layer 519 of the SOI wafer is used as the substrate on whichthe accelerometer, pressure sensor and microphone are formed. In thisexemplary embodiment, the handle layer is conductive and is formed ofsingle crystal silicon that is doped with dopants such as phosphorus,arsenic, antimony, boron among others. In this exemplary embodiment, thehandle layer serves as the substrate for each sensor on which the fieldregion and sensor region is formed. Thus, for the accelerometer, thehandle layer is used to support the vertical interconnects (TSV) totransfer the electrodes from the sensor region to the other surface ofthe handle layer, for subsequent connection to an interface circuit. Inthis exemplary embodiment, 650, 651 and 652 are the verticalinterconnects for the accelerometer. In the sensor region for theaccelerometer, the handle layer is used to support the static anddynamic structural components of the accelerometer. The handle layer forthe accelerometer in the sensor region also serves as a motion limitinglayer for the dynamic structural components. Thus, when a dynamicstructural component of the accelerometer moves towards the handlelayer, the motion of the dynamic structural component is stopped when itmakes contact with the handle layer below the dynamic structuralcomponent. Here the handle layer also performs the function of a motionlimiting layer in addition to providing support to the static anddynamic structural components of the accelerometer. When the static ordynamic structural component of the accelerometer is partially or whollyin contact with the handle layer, through the intermediate buried oxidestructural layer, it is supported by the handle layer by the formationof a support or anchor region. In this exemplary embodiment, the handlelayer in the accelerometer sensor region acts as motion limiting regionfor dynamic component 544 and as a support or anchor for the staticcomponents.

For the pressure sensor 504, the handle layer performs the function ofserving as a substrate for all the structural components of the pressuresensor. Thus, for the pressure sensor, in the field region, the handlelayer is used to support the vertical interconnects (TSV) to transferthe electrodes from the sensor region to the other surface of the handlelayer, for subsequent connection to an interface circuit. In thisexemplary embodiment, 653 and 654 are the vertical interconnects for theaccelerometer. In the sensor region of pressure sensor 504, the handlelayer is used to support the static and dynamic structural components ofthe pressure sensor. In this exemplary embodiment, the handle layer inthe sensor region is used as a support or anchor region. In this case,the handle layer acts as a support for the static reference electrode ofthe pressure sensor through the intermediate buried oxide structurallayer.

For the microphone 506, the handle layer performs the function ofserving as the substrate for all the structural components of themicrophone. Thus, for the microphone, in the field region, the handlelayer is used to support the vertical interconnects (TSV) to transferthe electrodes from the sensor region to the other surface of the handlelayer, for subsequent connection to an interface circuit. In thisexemplary embodiment, 655 and 656 are the vertical interconnects for thepressure sensor. In the sensor region of the microphone 506, the handlelayer is used support the static and dynamic structural components ofthe microphone. In this exemplary embodiment, the handle layer in themicrophone in the sensor region is used as a support or anchor region.In this case, the handle layer acts as a support for the staticreferences electrode of the microphone through the intermediate buriedoxide structural layer.

The buried oxide layer 518 shown in FIG. 6 is another structural layerthat is used in this exemplary embodiment for the implementation of theaccelerometer, pressure sensor and microphone. In this exemplaryembodiment, the buried oxide layer is an insulator that does not conductelectricity. The buried oxide layer is used for implementation in boththe field region and sensor region and for both static and dynamicstructural components. In the field region, the buried oxide layer isused to support the formation of the vertical interconnects. In thesensor region, the buried oxide layer is used for the formation of thestatic and dynamic components of the accelerometer, pressure sensor andmicrophone.

For the accelerometer 502, the buried oxide layer is used to support theformation of the vertical interconnects in the field region. The buriedoxide layer is partially removed to allow the formation of the verticalinterconnects through the device layer, the buried oxide layer and thehandle layer. In the sensor area of the accelerometer, the buried oxidelayer is used to form the static and dynamic structural components ofthe accelerometer. In the sensor region of the accelerometer, the buriedoxide layer is used to support the static components of theaccelerometer. The buried oxide layer component 523 and 524 forms theanchor or support for static components of the accelerometer. Thesestatic components 522 and 545 can be fixed electrodes of theaccelerometer that does not move with any input acceleration. Thus, 522and 545 can be a fixed structural component such as a finger, blade,plate and the like that serves as a fixed electrode for an element suchas a capacitor. The buried oxide component 525 and 526, form the anchoror support for a dynamic component of the accelerometer. The dynamicstructural component of the accelerometer consists of the proof massthat moves in response to the inertial force, the spring suspension thatprovides the flexibility to the proof mass to move in response to theinertial force. The spring suspension also connects the proof mass tothe anchor or support region that is supported by the buried oxidecomponent 525 and 526. The buried oxide layer is removed below the proofmass and the spring suspension so that the dynamic components can movein response to the inertial force. The buried oxide layer may also actas a dynamic structural component if small buried oxide components areallowed to remain attached to the underside of the dynamic componentssuch as the proof mass and suspension spring. In this case, the smallburied oxide layer components attached to the underside of the dynamiccomponents acts as a motion limiting stop, preventing the dynamiccomponents such as the proof mass and the suspension springs from cominginto contact directly with the handle layer.

For the pressure sensor 504, the buried oxide layer is used to supportthe formation of the vertical interconnects in the field region. Theburied oxide layer is partially removed to allow the formation of thevertical interconnects through the device layer, the buried oxide layerand the handle layer. In the sensor area of the pressure sensor, theburied oxide layer is used to form the static and dynamic structuralcomponents of the pressure sensor. In the sensor region of the pressuresensor, the buried oxide layer is used to support the static componentof the pressure sensor. The buried oxide layer component 530 forms theanchor or support for a static component of the pressure sensor.

For the microphone 506, the buried oxide layer is used to support theformation of the vertical interconnects in the field region. The buriedoxide layer is partially removed to allow the formation of the verticalinterconnects through the device layer, the buried oxide layer and thehandle layer. In the sensor area of the microphone, the buried oxidelayer is used to form the static and dynamic structural components ofthe microphone. In the sensor region of the microphone, the buried oxidelayer is used to support the static component of the microphone. Theburied oxide layer component 533 forms the anchor or support for astatic component of the microphone.

The active layer or device layer 517 as shown in FIG. 6 is the nextstructural layer used for the exemplary embodiment that is used for theimplementation of the accelerometer, pressure sensor and microphone. Theactive layer is used for each sensor device in both the field region andthe sensor region. The active layer is used for each sensor to implementboth the static and dynamic structural components of the accelerometer,pressure sensor and microphone. In this exemplary embodiment, the activelayer is a conductive layer and is formed of single crystal silicon andis doped with dopants such as phosphorus, antimony, arsenic, boron amongothers.

For the accelerometer 502, the active layer or device layer is used inboth the field region and sensor region to implement the static anddynamic structural components of the accelerometer. In the field region,the active layer is used to support the vertical interconnects that areused to connect the electrodes of the accelerometer to the interfacecircuit attached to the other surface of the handle layer. In thisexemplary embodiment, the active layer is used to support the verticalinterconnects by removing a portion of the active layer to form verticaltrenches and then refilling with an insulating layer and a conductivelayer. The vertical trenches are formed using DRIE (Deep Reactive IonEtching) to remove the active layer down to the buried oxide, removing aportion of the buried oxide using RIE (reactive ion etching), andremoving a portion of the handle layer using DRIE (Deep Reactive IonEtching). The sidewalls of the trenches are lined with an insulatinglayer such as silicon dioxide and then the trenches are filled using aconductive layer such as in-situ doped LPCVD polycrystalline silicon.

For the accelerometer 502, the active layer or device layer is used inthe sensor region to form the static and dynamic structural componentsof the accelerometer. In this exemplary embodiment, the accelerometeruses capacitive transduction to convert the input acceleration into anequivalent electrical capacitance.

For the accelerometer, the structural component 544 is the dynamiccomponent that moves under the influence of an input acceleration thatis applied to the accelerometer. In this exemplary embodiment, the inputacceleration is applied laterally to the sensor and as such the sensoracts as a lateral accelerometer. The dynamic structural component 544consists of a portion of the active layer or device layer that isseparated from the rest of the active or device layer by the trenches671 and 672. In this exemplary embodiment, the dynamic structuralcomponent is suspended by a spring-like structure 574, which isconnected at the other end to another portion of the active or devicelayer to form an anchor structure or support structure. The dynamicstructural component 544 is formed above the handle layer and a regionof the buried oxide is removed below the dynamic structural component544. Thus, for the accelerometer, the portion of the active or devicelayer is used to form the dynamic structural component 544 that isconnected to the spring suspension 574 which is connected at the otherend to an anchor structure that is supported by another portion of theactive or device layer. Since the buried oxide region below the portionof the active or device layer is removed, the dynamic structuralcomponent 544 is capable of motion under the influence of an inputlateral acceleration. The portion of the active or device layer that isused to form the dynamic structural component may consist of proof mass,fingers, frames, blades, electrodes and the like that move under theinfluence of an input acceleration. The portion of the active layer ordevice layer that forms the dynamic structural component may also beused to form a suspension or spring structure for the accelerometer.

The active layer or device layer for the accelerometer may also be usedfor forming static structural components for the accelerometer. Thestatic structural components of the accelerometer do not move inresponse to the input acceleration. These static structural componentsare supported by the handle layer with a partial or complete region ofthe buried oxide layer. In the exemplary embodiment, the active ordevice layer is used for formation of the static structural components542, which are supported by the handle layer with buried oxide layercomponents 522, static component 543 supported by the handle layer withburied oxide component 523, static component 545 supported by the handlelayer with buried oxide component 524, and static component 546supported by the handle layer with buried oxide component 525. In thisexemplary embodiment, the active or device layer is used to form astatic structural component such as a finger, plate, blade and the likeof the accelerometer. Similarly, the active or device layer is used toform another static structural component such as a finger, plate, bladeand the like of the accelerometer. The static structural component 543is anchored to the handle layer by a portion of the buried oxide layer523 and similarly the static structural component 545 is anchored to thehandle layer by a portion of the buried oxide layer 524.

In this exemplary component, the active device layer structuralcomponents 543, 544, and 545 are used to sense and transduce the inputacceleration into an equivalent electrical parameter. In thisembodiment, the transduction principle that is used is capacitive,meaning that the input acceleration is converted or transduced by theaccelerometer into an equivalent capacitance. The capacitive transduceris formed by 543 and 545, which forms the two fixed plates of thecapacitance, since they are anchored to the handle layer by the buriedoxide regions 523 and 524 respectively. The dynamic structural component544 forms the moving plate of the capacitance that is formed between thestatic structural components 543 and 545 that form the static or fixedplates of the capacitance. For convenience, the capacitance structure isassumed to be a parallel plate capacitance whose capacitance isdetermined by formula

$C = \frac{ɛ\; A}{d}$

where ε is the dielectric constant, A is the area of each plate and d isthe gap spacing between the plates. The capacitance that is formedbetween 543 and 544 is defined by the spacing 671 between 543 and 544and the area of overlap of the plates formed by 543 and 544 into theplane of the drawing. Similarly, the capacitance that is formed between544 and 545 is defined by the spacing 672 between 544 and 545 and thearea of overlap of the plates into the plane of the drawing. Thus, 543,544 and 545 form two capacitances with 543 and 545 as the fixed platesor electrodes and 544 as the moving or dynamic plate or electrode.

When an input acceleration is applied to the accelerometer in adirection laterally, the dynamic plate moves under the inputacceleration. In the exemplary device, if the input acceleration isapplied from right to left in the plane of the sensor, the dynamic platemoves towards the fixed plate or electrode 543. Thus, the gap 671between the static plate and the moving plate is decreased and the gap672 between the static plate 543 and the moving plate 544 is increasedby the same lateral distance. The decrease in the distance between thestatic plate 543 and the dynamic plate 544 means that the capacitancebetween 543 and 544 is increased. The increase in the distance betweenstatic plate 545 and the moving or dynamic plate 544 means that thecapacitance between 544 and 545 is decreased. The change in capacitancebetween 543 and 544 or between 544 and 545 in the presence of theapplied acceleration and from a condition of no acceleration is ameasure of the applied acceleration. Thus the method of capacitancetransduction is able to convert the applied acceleration into anequivalent electrical capacitance change. Thus, the dynamic and staticstructural components formed by the active or device layer are used forthe formation of a capacitance transducer to convert the inputmechanical acceleration to an equivalent electrical capacitance change.This change in the capacitance is used as the input for the interfacecircuit to which the accelerometer is connected.

For the pressure sensor 504, the active or device layer is used instructural components in both the field region and the sensor region toimplement the static and dynamic structural components. In thisexemplary embodiment, in the field region, the active layer is used tosupport the vertical interconnects that are used to connect theelectrodes of the pressure sensor to the interface circuit connected tothe other side of the handle layer. In this exemplary embodiment, theactive layer is used to support the vertical interconnects by removing aportion of the active layer to form vertical trenches and then refillingwith an insulating layer and a conductive layer. The vertical trenchesare formed using DRIE (Deep Reactive Ion Etching) to remove the activelayer down to the buried oxide, removing a portion of the buried oxideusing RIE (reactive ion etching), and using a portion of the handlelayer using DRIE (Deep Reactive Ion Etching). The sidewalls of thetrenches are lined with an insulating layer such as silicon dioxide andthen the trenches are filled using a conductive layer such as in-situdoped LPCVD polycrystalline silicon.

For the pressure sensor, the active layer or device layer is used in thesensor region to form a static structural component of the pressuresensor. In this exemplary embodiment, the pressure sensor usescapacitive transduction to convert the input pressure into an equivalentelectrical capacitance. In this exemplary embodiment, the capacitivetransduction is implemented using a static structural plate that servesas a reference electrode and forming another structural element thatforms a diaphragm or membrane with a gap between the static plate andthe whole structure enclosing a cavity that is sealed in vacuum. When apressure is applied on the diaphragm, it deflects towards the static orreference plate, thereby changing the gap between the static plate andthe diaphragm.

The diaphragm and the static reference plate form a capacitance wherethe area of overlap between the static plate and the diaphragm and thegap between the two determines the capacitance between the two. For easeof analysis, the capacitance between the static plate and the dynamicdiaphragm is approximated by a parallel plate capacitance in which case,the capacitance is represented by the formula

$= \frac{ɛ\; A}{d}$

where ε is the dielectric constant, A is the area of each plate and d isthe gap spacing between the plates. Thus, if the pressure applied on thediaphragm is increased, the diaphragm deflects more towards the staticplate and the gap between the diaphragm and the static reference plateis decreased and the capacitance increases. If the pressure applied onthe diaphragm is decreased, the diaphragm deflects less towards thestatic plate and the gap between the static reference plate and thediaphragm increases and the capacitance decreases. Thus, the change inthe capacitance is representative of the change in the pressure appliedto the diaphragm. This change in the capacitance is converted to anequivalent electrical parameter that represents the change in thepressure that is being measured. Thus the method of capacitancetransduction is able to convert the applied pressure into an equivalentelectrical capacitance change. Thus, the static structural componentformed by the active or device layer is used for the formation of acapacitance transducer to convert the input mechanical pressure to anequivalent electrical capacitance change.

In the exemplary embodiment, the portion of the active or device layer550, is used as a static structural component of the pressure sensorusing capacitance transduction. The static structural component formedby the portion of the active layer 550, is supported by the portion ofthe buried oxide layer 529 that is attached to the handle layer 600.

For the microphone 506, the active or device layer is used in structuralcomponents in both the field region and the sensor region to implementthe static and dynamic structural components. In this exemplaryembodiment, in the field region, the active layer is used to support thevertical interconnects that are used to connect the electrodes of themicrophone to the interface circuit connected to the other side of thehandle layer. In this exemplary embodiment, the active layer is used tosupport the vertical interconnects by removing a portion of the activelayer to form vertical trenches and then refilling with an insulatinglayer and a conductive layer. The vertical trenches are formed usingDRIE (Deep Reactive Ion Etching) to remove the active layer down to theburied oxide, removing a portion of the buried oxide using RIE (reactiveion etching), and using a portion of the handle layer using DRIE (DeepReactive Ion Etching). The sidewalls of the trenches are lined with aninsulating layer such as silicon dioxide and then the trenches arefilled using a conductive layer such as in-situ doped LPCVDpolycrystalline silicon.

For the microphone 506, the active layer or device layer is used in thesensor region to form a static structural component of the microphone.In this exemplary embodiment, the microphone uses capacitivetransduction to convert the input acoustic or audio waves into anequivalent electrical capacitance. In this exemplary embodiment, thecapacitive transduction is implemented using a static structural platethat serves as a reference electrode and forming another structuralelement that forms a membrane with a gap between the static plate andthe whole structure enclosing a cavity. When sound waves impinge on themembrane, pressure is applied on the membrane, it vibrates and deflectswith references to the static or reference plate, thereby changing thegap between the static plate and the membrane.

The membrane and the static reference plate form a capacitance where thearea of overlap between the static plate and the membrane and the gapbetween the two determines the capacitance between the two. For ease ofanalysis, the capacitance between the static plate and the dynamicmembrane is approximated by a parallel plate capacitance in which case,the capacitance is represented by the formula

$C = \frac{ɛ\; A}{d}$

where ε is the dielectric constant, A is the area of each plate and d isthe gap spacing between the plates. Thus, if the acoustic pressure dueto an impinging sound wave applied on the diaphragm is increased, themembrane deflects more towards the static plate and the gap between themembrane and the static reference plate is decreased and the capacitanceincreases. If the acoustic pressure applied on the membrane isdecreased, the membrane deflects less towards the static plate and thegap between the static reference plate and the membrane increases andthe capacitance decreases. Thus, the change in the capacitance isrepresentative of the change in the pressure applied to the membrane bythe impinging sound wave. This change in the capacitance is converted toan equivalent electrical parameter that represents the change in theacoustic pressure that is being applied by the impinging sound wave.Thus the method of capacitance transduction is able to convert theapplied sound wave into an equivalent electrical capacitance change.Thus, the static structural component formed by the active or devicelayer is used for the formation of a capacitance transducer to convertthe input sound wave to an equivalent electrical capacitance change.

In the exemplary embodiment, the portion of the active or device layer554, is used as a static structural component of the microphone usingcapacitance transduction. The static structural component formed by theportion of the active layer 554, is supported by the portion of theburied oxide layer 610 n that is attached to the handle layer 600.

In this exemplary embodiment, the active or device layer is used in thedifferent sensors for formation of different structural components thatenable the formation of static and dynamic structural components of theaccelerometer 502, pressure sensor 504, and microphone 506. For eachsensor, the active or device layer is used to support the formation ofthe vertical interconnects to connect each sensor to an interfacecircuit. Thus, vertical interconnects are used to connect theaccelerometer, pressure sensor and microphone to the opposite side ofthe handle layer to an interface circuit. The active or device layer isused to form the static electrode 543 and 545 of the accelerometer, thedynamic structural component 544 such as the proof mass, sensing finger,suspension string, the anchor or static support for the dynamiccomponents, the motion limiting stops for the dynamic structuralcomponents. The same active or device layer is used to form a portion ofthe static or reference electrode 550 of the pressure sensor and thestatic or reference electrode 554 of the microphone. It will be evidentto those skilled in the arts that the active or device layer can be usedfor implementing for the static and dynamic structural components ofdifferent sensors that respond to different input stimulus.

The nitride layer 565 is another layer used in the exemplary embodimentof implementation of the accelerometer 502, pressure sensor 504 andmicrophone 506 using parallel design and fabrication technology andmethod. The nitride layer is used in both the field region and sensorregion for the implementation of the accelerometer 502, pressure sensor504 and microphone 506. In the field region, the nitride layer 565 isused to protect and support the vertical interconnects as well as toprovide electrical isolation for the static and dynamic structuralcomponents of the accelerometer 502, pressure sensor 504 and microphone506.

In the exemplary embodiment, the nitride layer 565 is used to supportand protect the vertical interconnects in the field region and toprovide mechanical support and electrical isolation for the static anddynamic structural components in the sensor region.

In the field region for the accelerometer, the nitride layer is used toprotect the vertical interconnects 650, 651 and 652 that are used toconnect the electrodes of the accelerometer to the interface circuitthat is attached to the opposite surface of the handle layer. Since thevertical interconnects are formed by a lining of insulating layer suchas silicon dioxide that encloses a layer of conducting material such asdoped polycrystalline silicon, it is essential to protect the silicondioxide layer from fabrication steps that uses chemicals such as HF orBHF in the formation of the accelerometer. The nitride layer must beremoved over the conducting layer forming the vertical interconnect sothat it can be connected to the different electrodes of the sensor. Inthe field region for each vertical interconnect, the nitride layer isremoved so that it covers the top surface of the active layer in thefield region and the edges of the silicon oxide liner is not exposed tothe chemicals such as HF or BHF. The nitride layer is also used tosupport the static structural components of the accelerometer to providean anchor and also electrically isolation. The static structuralcomponent of the accelerometer that is supported by the nitride layer inthe field region is the cap 593, which is formed to protect the staticand dynamic structural components from the assembly and packagingprocesses. The cap structure is anchored or supported by the nitridelayer 560 and 561 to provide mechanical support. Thus, 560 and 561 areused in the field regions of the accelerometer to provide isolation andprotect the vertical interconnects 650, 651 and 652.

The nitride structural layer 565 can also be used in the accelerometerin the sensor region to form and support the static and dynamicstructural components. The nitride layer may be patterned on top of thestatic or dynamic structural components formed by the active or devicelayer, and can provide mechanical support or electrical isolation. Thenitride layer may be used in the sensor region for the formation ofpillars, posts, walls and the like to provide mechanical support for thecap structure.

For the pressure sensor 504, the nitride layer represented by 561 isused in the field region and the sensor region to form and support thestatic and dynamic structural components of the sensor.

In the field regions 510 and 512 for the pressure sensor as shown inFIG. 5A, the nitride layer is used to protect the vertical interconnectsthat are used to connect the electrodes of the pressure sensor to theinterface circuit that is attached to the opposite surface of the handlelayer. Since the vertical interconnects are formed by a lining ofinsulating layer such as silicon dioxide that encloses a layer ofconducting material such as doped polycrystalline silicon, it isessential to protect the silicon dioxide layer from fabrication stepsthat uses chemicals such as HF or BHF in the formation of theaccelerometer. The nitride layer must be removed over the conductinglayer forming the vertical interconnect so that it can be connected tothe different electrodes of the sensor. In the field region for eachvertical interconnect, the nitride layer is removed so that it coversthe top surface of the active layer in the field region and the edges ofthe silicon oxide liner is not exposed to the chemicals such as HF orBHF. The nitride layer is also used to support the dynamic structuralcomponent of the pressure sensor to provide an anchor and alsoelectrically isolation. The dynamic structural component of the pressuresensor that is supported by the nitride layer in the field region is thediaphragm 599, which is formed to sense the pressure by deflection. Thediaphragm is anchored or supported by the nitride layer 561 and 562 toprovide mechanical support and electrical isolation. Thus, 561 and 562are used in the field regions of the pressure sensor to provideisolation and protect the vertical interconnects 653 and 654.

The nitride structural layer 565 can also be used in the pressure sensorin the sensor region to form and support the static and dynamicstructural components. The nitride layer may be patterned on top of thestatic or dynamic structural components formed by the active or devicelayer, and can provide mechanical support or electrical isolation. Thenitride layer may be used in the sensor region for the formation ofpillars or posts to provide mechanical support for the static anddynamic structural components.

For the microphone 506, the nitride layer is used in the field regionand the sensor region to form and support the static and dynamicstructural components of the sensor.

In the field regions 513 and 515 as shown in FIG. 5A, for the microphone506, the nitride layer is used to protect the vertical interconnectsthat are used to connect the electrodes of the microphone to theinterface circuit that is attached to the opposite surface of the handlelayer. Since the vertical interconnects are formed by a lining ofinsulating layer such as silicon dioxide that encloses a layer ofconducting material such as doped polycrystalline silicon, it isessential to protect the silicon dioxide layer from fabrication stepsthat uses chemicals such as HF or BHF in the formation of theaccelerometer. The nitride layer must be removed over the conductinglayer forming the vertical interconnect so that it can be connected tothe different electrodes of the sensor. In the field region for eachvertical interconnect, the nitride layer is removed so that it coversthe top surface of the active layer in the field region and the edges ofthe silicon oxide liner is not exposed to the chemicals such as HF orBHF. The nitride layer is also used to support the dynamic structuralcomponent of the microphone to provide an anchor and also electricallyprovide electrical isolation. The dynamic structural component of themicrophone that is supported by the nitride layer in the field region isthe membrane 605, which is formed to sense the acoustic pressure bydeflection. The membrane is anchored or supported by the nitride layer562 and 563 to provide mechanical support and electrical isolation.Thus, 562 and 563 are used in the field regions of the microphone toprovide isolation and protect the vertical interconnects 655 and 656.

The nitride structural layer can also be used in the microphone in thesensor region to form and support the static and dynamic structuralcomponents. The nitride layer may be patterned on top of the static ordynamic structural components formed by the active or device layer, andcan provide mechanical support or electrical isolation. The nitridelayer may be used in the sensor region for the formation of pillars orposts to provide mechanical support for the static and dynamicstructural components.

A polycrystalline silicon or polysilicon layer 660 is another structurallayer used in the implementation of the multiple sensors that areco-designed and use a parallel fabrication process. In the exemplaryembodiment 500, the polysilicon layer is used in both the field regionand sensor region of the accelerometer 502, pressure sensor 504 andmicrophone 506 and for the implementation of static and dynamicstructural components for the accelerometer 502, pressure sensor 504 andmicrophone 506. The polysilicon layer 660 is a conductive layer and isdoped with dopants such as phosphorus, arsenic, antimony, boron and thelike. The doping of the polysilicon layer may be in-situ (as it is beingdeposited), ion-implantation followed by an anneal to distribute thedopants, with a solid state doping source followed by an anneal todistribute the dopants and other methods to dope polysilicon layers.

In the exemplary embodiment, the polysilicon layer 660 is used in thefield region and sensor region for the implementation of static anddynamic structural components of the accelerometer 502. In the fieldregions 507 and 509, the polysilicon structural layer is used to formthe interconnects from the electrodes of the sensor in the sensor regionto the vertical interconnects which connect the sensor electrodes to theinterface circuit that is attached to the opposite surface of the handlelayer. The structural layer 660 is used to form the bridge structuralcomponents 571 and 575 that connect the static and dynamic structuralcomponents of the accelerometer. The bridge structure 571 connects thestatic structural component 543 to the vertical interconnect 651 in thefield region. The bridge structure 575 connects the dynamic structuralcomponent 544 to the vertical interconnect 652 in the field region. Inthe field region, the polysilicon structural layer may also contain astructural component that is supported on the nitride structural layerand connected to a bridge structural component at one end and to thevertical interconnect 651 and 652 at the other end. Thus, thepolysilicon structural layer may serve as a planar interconnect betweenthe bridge structural component 571 and the vertical interconnectstructure 651.

In the sensor region of the accelerometer 502, in the exemplaryembodiment, the polysilicon structural layer 660 is used for theformation of static and dynamic structural components of theaccelerometer. In the sensor region, the polysilicon structuralcomponent 575 is used to serve to form a bridge structure to connect thedynamic structural component 544 to the vertical interconnect 652. Thisstructural component 574 also forms a part of the dynamic structuralcomponent of the accelerometer by providing a suspension or spring using574 for the dynamic structural component of the accelerometer. Thedynamic structural component of the accelerometer is able to move underthe influence of the input acceleration force and can constitute theproof mass, fingers for sensing, plate structures, suspension spring.The polysilicon structural layer is used to form the suspension spring574 which also serves as a bridge to connect the dynamic structuralcomponent of the accelerometer to the vertical interconnect. The part ofthe suspension spring 573 and 576 that is connected to the verticalinterconnect also serves as the anchor or support for the dynamicstructural component of the accelerometer.

In the sensor region of the accelerometer 502, in the exemplaryembodiment, the polysilicon structural layer is used to connect thestatic structural components to the vertical interconnects. Thepolysilicon layer may also be used to connect different staticstructural components by using a bridge structure, and which are at thesame electrical potential. In the sensor region, the polysiliconstructural layer is used to form a bridge between the static structuralcomponent 543 and the vertical interconnect 651. The polysiliconstructural layer 660 may also be used to form part of the staticstructural component of the accelerometer by forming fingers or platesthat serve as reference electrodes of the accelerometer 502.

In the sensor region, the polysilicon structural layer may also be usedas a motion stop to prevent excessive motion of the dynamic structuralcomponent of the accelerometer under the input acceleration. Thepolysilicon layer may be used in the static and dynamic structuralcomponents of the motion limiting stop structure of the accelerometer.

In the sensor region, the polysilicon structural layer may also be usedfor formation of pillars, posts, walls and the like to support theprotective cap that is formed in subsequent steps in the fabrication ofthe accelerometer. These pillars, posts, walls are formed with staticstructural components of the accelerometer and enable the cap structureto protect the static and dynamic structural components of theaccelerometer from the effects of assembly and packaging.

In the exemplary embodiment, the polysilicon structural layer is used inthe pressure sensor 504 in both the field region and region forformation of both the static and dynamic structural components.

In the field regions 510 and 512, the polysilicon structural layer 660is used to form the interconnects from the electrodes of the sensor inthe sensor region to the vertical interconnects which connect the sensorelectrodes to the interface circuit that is attached to the oppositesurface of the handle layer. The structural layer 660 is used to formthe bridge structural components that connect the static and dynamicstructural components of the pressure sensor. The bridge structure 577and 578 connects the static structural component 580 to the verticalinterconnect 654 in the field region. In the field region, thepolysilicon structural layer may also contain a structural componentthat is supported on the nitride structural layer and connected to abridge structural component at one end and to the vertical interconnect654 at the other end. Thus, the polysilicon structural layer may serveas a planar interconnect between the bridge structural component 580 andthe vertical interconnect structure 654.

In the sensor region of the pressure sensor 504, in the exemplaryembodiment, the polysilicon structural layer 660 is used for theformation of static and dynamic structural components of the pressuresensor. In the sensor region, the polysilicon structural component 580along with 578 is used to serve to form a bridge structure to connectthe static structural component to the vertical interconnect 654. Thepolysilicon structural layer is used to form the static structuralcomponent 580 that forms the static or fixed or reference plate of thepressure sensor. This static or fixed reference plate is attached to theunderlying active layer or device layer by a number of posts or pillars579, 581, and 582. This static or fixed reference plate is alsoconnected to the bridge structure formed by the polysilicon structurallayer to the field region so that it is connected to the verticalinterconnect 654. The static structural component 580 that forms thefixed or reference plate of the pressure sensor may be connectedelectrically to the underlying component of the device or active layerif the nitride structural layer is removed and the anchors 579, 581 and582 attach directly to the static structural component 550 formed by thedevice or active layer. In this present embodiment, the static orreference plate formed by the polysilicon structural layer 580 isattached by a number of pillars or posts 579, 581 and 582 to the staticstructural component formed by the device layer. Thus, the two staticcomponents 580 and 550 are both electrically and mechanically connectedand together form the static or reference plate or electrode of thepressure sensor.

In another embodiment, the fixed or reference plate formed by thepolysilicon structural layer may be isolated from the underlying staticstructural component formed by the active or device layer. In thisembodiment, the nitride structural layer is not removed between thepillars or posts formed by the polysilicon structural layer and theunderlying device or active layer. In this embodiment, the staticstructural component 580 formed by the polysilicon structural layer ismechanically connected to the underlying static structural component 550formed by the active or device layer but electrically isolated from itdue to the presence of the intermediate nitride structural layer.

In yet another embodiment, the static or reference plate formed by thepolysilicon structural layer may be attached directly to the underlyingstatic structural component formed by the active or device structurallayer, without any pillars or posts. In this embodiment, the static orreference plate of the pressure sensor is formed on the surface of thestatic component formed by the active or device layer. If theintermediate nitride structural layer is removed between the polysiliconstructural component 580 and the static component formed by the activeor device layer 550, the two static components 580 and 550 are bothelectrically and mechanically connected and together form the static orreference plate or electrode of the pressure sensor. If the intermediatenitride structural layer is present between the polysilicon structuralcomponent 580 and the static component formed by the active or devicelayer 550, the two static components 580 and 550 are mechanicallyconnected but electrically isolated and only polysilicon staticstructural component 580 forms the static or reference plate orelectrode of the pressure sensor.

In the exemplary embodiment, the polysilicon structural layer is used inthe microphone 506 in both the field region and region for formation ofboth the static and dynamic structural components.

In the field regions 513 and 515, the polysilicon structural layer isused to form the interconnects from the electrodes of the sensor in thesensor region to the vertical interconnects which connect the sensorelectrodes to the interface circuit that is attached to the oppositesurface of the handle layer. The structural layer 660 is used to formthe bridge structural components that connect the static and dynamicstructural components of the microphone. The bridge structure 584connects the static structural component 586 to the verticalinterconnect 656 using 583 in the field region. In the field region, thepolysilicon structural layer may also contain a structural componentthat is supported on the nitride structural layer and connected to abridge structural component at one end and to the vertical interconnect656 at the other end. Thus, the polysilicon structural layer may serveas a planar interconnect between the bridge structural component 586 andthe vertical interconnect structure 656.

In the sensor region 514 of the microphone 506, in the exemplaryembodiment, the polysilicon structural layer 660 is used for theformation of static and dynamic structural components of the microphone.In the sensor region, the polysilicon structural component 586 is usedto serve to form a bridge structure using 584 to connect the staticstructural component to the vertical interconnect 656. The polysiliconstructural layer is used to form the static structural component 586that forms the static or fixed or reference plate of the microphone.This static or fixed reference plate 586 is attached to the underlyingactive layer or device layer by a number of posts or pillars 585, 587,and 588. This static or fixed reference plate is also connected to thebridge structure formed by the polysilicon structural layer to the fieldregion so that it is connected to the vertical interconnect 656. Thestatic structural component 586 that forms the fixed or reference plateof the microphone may be connected electrically to the underlyingcomponent of the device or active layer 554 if the nitride structurallayer is removed and the anchors 585, 587 and 588 attach directly to thestatic structural component 554 formed by the device or active layer. Inthis present embodiment, the static or reference plate formed by thepolysilicon structural layer is attached by a number of pillars or poststo the static structural component formed by the device layer. Thus, thetwo static components 586 and 554 are both electrically and mechanicallyconnected and together form the static or reference plate or electrodeof the microphone.

In another embodiment, the fixed or reference plate formed by thepolysilicon structural layer may be isolated from the underlying staticstructural component formed by the active or device layer. In thisembodiment, the nitride structural layer is not removed between thepillars or posts formed by the polysilicon structural layer and theunderlying device or active layer. In this embodiment, the staticstructural component 586 formed by the polysilicon structural layer ismechanically connected to the underlying static structural component 554formed by the active or device layer but electrically isolated from itdue to the presence of the intermediate nitride structural layer.

In yet another embodiment, the static or reference plate formed by thepolysilicon structural layer may be attached directly to the underlyingstatic structural component formed by the active or device structurallayer, without any pillars or posts. In this embodiment, the static orreference plate of the microphone is formed on the surface of the staticcomponent formed by the active or device layer. If the intermediatenitride structural layer is removed between the polysilicon structuralcomponent 586 and the static component formed by the active or devicelayer 554, the two static components 586 and 554 are both electricallyand mechanically connected and together form the static or referenceplate or electrode of the microphone. If the intermediate nitridestructural layer is present between the polysilicon structural component586 and the static component formed by the active or device layer 554,the two static components 586 and 554 are mechanically connected butelectrically isolated and only polysilicon static structural component586 forms the static or reference plate or electrode of the microphone.

The polysilicon structural layer 661 is another layer used for theimplementation of the exemplary embodiment using parallel designmethodology for the device 500 with co-designed accelerometer 502,pressure sensor 504 and microphone 506. This polysilicon structurallayer is used in both the field region and sensor region for theformation of static and dynamic structural components of theaccelerometer 502, pressure sensor 504 and microphone 506. Thepolysilicon layer 661 is a conductive layer and is doped with dopantssuch as phosphorus, arsenic, antimony, boron and the like. The doping ofthe polysilicon layer may be in-situ (as it is being deposited),ion-implantation followed by an anneal to distribute the dopants, with asolid state doping source followed by an anneal to distribute thedopants and other methods to dope polysilicon layers.

In the accelerometer 502, the polysilicon structural layer 661 is usedin the field region 507 and 509 and sensor region 508 for the formationof static and dynamic structural components.

In the field region of the accelerometer 507 and 509, the polysiliconstructural layer 661 is used to form the anchor or support of the capstructure of the accelerometer. The cap structure is supported on thenitride structural layer by the anchor or support components formed inthe field region 590 and 595. The polysilicon structural layer 661 isalso used, in the exemplary embodiment, to connect the cap structure tothe vertical interconnect that is used to connect the cap structure toan electrode of the interface circuit that is attached to the other sideof the handle layer. Thus, the polysilicon structural layer 661 is usedto form a contact to the vertical interconnect 651. In anotherembodiment, the structural layer 661 may be used to form a planarinterconnect structure that is supported on the nitride structural layer750 and connects the cap structure to the vertical interconnect 651.

In the sensor region of the accelerometer 502, the polysiliconstructural layer 661 is used to form a cap structure 593 that is formedon top of static and dynamic structural components of the accelerometer.Since the accelerometer contains dynamic structural components that moveunder the influence of an input acceleration and contains small gapsthat enable the dynamic structural components such as the proof mass,fingers, spring suspension to move and also contains static structuralcomponents such as fingers or plates that form capacitances where oneplate (the dynamic structural components) moves relative to anotherplate (the static structural components), it is necessary to protectthese static and dynamic structural components of the accelerometer fromthe deleterious effects of assembly and packaging. When the fabricationprocess of the device 500 is completed, it is prepared for attaching tothe interface circuit and then further for assembly in a package. Theseprocesses require that the device 500 be able to withstand suchprocesses such as wafer thinning (grinding, etching), sawing (where thewafer is singulated to individual die), die bond (where the die isbonded to the interface circuit), die attach (where the die is attachedto a package), rinsing (with water and other chemicals). These processescan cause generation of particles that can lodge in the small gapsbetween the static and dynamic structural components of the sensorsformed by device 500. These processes may also cause the liquids (waterand other chemicals) to which the static and dynamic structuralcomponents are exposed to generate various surface forces causingsurface tension, adhesion, van der Waals forces causing the sensor tofail due to phenomena such as stiction, corrosion etc.

The polysilicon structural layer 661 is used to form a protective capstructure that surrounds all the static and dynamic structuralcomponents of the accelerometer 502, and prevents the exposure of thesmall gaps between the static and dynamic structural components of theaccelerometer to the assembly and packaging processes. Thus, thepolysilicon structural layer is used to form the protective capstructure 593 over the static and dynamic structural components of theaccelerometer. Thus, in the sensor region of the accelerometer 508, thepolysilicon layer 661 is used to form the cap structural component 593that serves to protect the static and dynamic structural components ofthe accelerometer. The cap structural component 593 is a staticcomponent that does not move relative to the static or dynamicstructural component of the sensor region of the accelerometer.

In the sensor region, the cap structural component 593 formed by thepolysilicon structural layer 661 can also be used to form pillars, post,walls and the like to increase the mechanical strength and resistance tothe assembly and packaging processes. Thus, while the cap structure 593is supported by the anchor region in the periphery, it can be used inthe sensor region to form pillars, posts and walls to improve themechanical strength of the cap structure. These static structuralcomponents such as pillars, posts and walls are formed on top of otherstatic components of the accelerometer which as supported by thepolysilicon structural layer, nitride structural layer, active layer,buried oxide layer, handle layer.

In the sensor region of the accelerometer 502, the polysiliconstructural layer can also be used in the cap structural component to actas a motion stop for the dynamic structural component of theaccelerometer. Thus, the cap structural component 593 may also serve tolimit the motion of the dynamic structural components of theaccelerometer under an excessive input acceleration or shock.

The polysilicon structural layer 661 may also be used to form etch holes592 and 594 in the accelerometer 502. These are openings in the capstructural component 593 and can be formed in both the field region andthe sensor region. The polysilicon structural layer is removed in thecap structural component so as to provide access to the sacrificialoxide structural layers (not shown in FIG. 5). In this exemplaryembodiment, the polysilicon structural layer is removed to form the etchholes 592 and 594 in the field region. In another embodiment, the etchholes in the polysilicon structural layer 661 can be formed in thesensor region. These etch holes in the polysilicon cap structuralcomponent are then sealed using another structural layer to form asealed cavity.

In the pressure sensor 504, the polysilicon structural layer 661 is usedin the field region 510 and 512 and sensor region 511 for the formationof static and dynamic structural components.

In the field regions 510 and 512 of the pressure sensor 504, thepolysilicon structural layer 661 is used to form the anchor or supportof the pressure sensor diaphragm. The diaphragm is supported on thenitride structural layer by the anchor or support components 597 and 601formed in the field region. The polysilicon structural layer 661 is alsoused, in the exemplary embodiment, to connect the diaphragm to thevertical interconnect that is used to connect the diaphragm to anelectrode of the interface circuit that is attached to the other side ofthe handle layer. Thus, the polysilicon structural layer 661 is used toform a contact 597 to the vertical interconnect 653. In anotherembodiment, the structural layer 661 may be used to form a planarinterconnect structure that is supported on the nitride structural layer561 and connects the diaphragm to the vertical interconnect 653.

In the sensor region 511 of the pressure sensor 504, the polysiliconstructural layer 661 is used to form the dynamic structural component ofthe pressure sensor. This dynamic structural component of the pressuresensor is the diaphragm 599 that responds to the ambient pressureapplied by the fluid in contact with the diaphragm. The polysiliconstructural layer 661 is used to form the diaphragm 599 of the pressuresensor that moves under an applied pressure by being supported by ananchor region that contacts the underlying nitride structural layer inits periphery and then forming a gap from the static or referencestructural component 580 and 550 of the pressure sensor which encloses acavity that is sealed in vacuum. Thus, the diaphragm 599 of the pressuresensor encloses a cavity that is at a pressure lower than atmosphericpressure (range). Thus, the pressure inside the cavity provides areference pressure applied to one side of the pressure sensingdiaphragm.

Since the side of the pressure sensor diaphragm that encloses the staticor reference plate of the pressure sensor is at a low pressure (vacuum),and the opposite side of the pressure sensor diaphragm is at the ambientpressure, the difference of the pressure applied on the pressure sensordiaphragm can cause the deflection of the diaphragm. The amount ofdeflection of the pressure sensor diaphragm is governed by materialproperties and geometrical dimensions of the pressure sensor diaphragm.The deflection is dependent on the thickness of the polysiliconstructural layer 661, the geometric dimensions of the pressure sensordiaphragm, the material properties of the polysilicon structural layersuch as modulus of elasticity, Poisson's ratio etc. The pressure sensordiaphragm may have different shapes depending on the design and theapplication for which the pressure sensor is intended to be used. Thepressure sensor may be circular, square, rectangular, octagonal etc. inshape. In the exemplary embodiment, the shape of the diaphragm isassumed to be circular. In this case, the size (radius) is chosen tohave a maximum deflection for the range of pressure that is to bemeasured by the pressure sensor.

In the sensor region of the pressure sensor, the polysilicon structurallayer 661 thus is used to form the diaphragm, the dynamic structuralcomponent 599. The pressure sensor in this exemplary embodiment usescapacitance transduction to convert the pressure being measured into anequivalent electrical parameter. In this exemplary embodiment, thedynamic structural component which is the diaphragm is separate by asmall gap from the static structural component or the reference plate orelectrode 580 and 550 formed by the polysilicon structural layer and theactive or device structural layer. Thus, the diaphragm 599 forms a plateof a capacitance that is capable of movement (deflection) under theinfluence of an applied pressure. The structural component 580 and 550forms the static or reference plate of the capacitance formed with thediaphragm. For ease of analysis, the capacitance is considered to be aparallel plate capacitance with the diaphragm forming one plate orelectrode of the capacitance and the reference or static plate formingthe other plate or electrode of the parallel plate capacitance. Thecapacitance is defined by the formula

$C = \frac{ɛ\; A}{d}$

where ε is the dielectric constant, A is the area of each plate and d isthe gap spacing between the plates. When the dynamic component of thepressure sensor, which is the diaphragm, moves down (deflects downtowards the reference plate) due to an increase in the ambient pressure,the gap between the diaphragm and the static reference plate isdecreased and the capacitance is increased. The change in thecapacitance is equivalent to the change in the pressure applied to thediaphragm from an equilibrium value or reference pressure. If thepressure applied on the diaphragm (which is the dynamic component) isdecreased, the diaphragm moves up (deflects away from the referenceplate) and the gap between the diaphragm and the reference plate isincreased. The increase in the gap between the diaphragm and the staticor reference plate decreases the capacitance and the change incapacitance is equivalent to the change in the pressure applied to thediaphragm from an equilibrium value or reference pressure. Other methodsof transduction may also be used to convert the deflection of thediaphragm to an equivalent electrical signal. These other transductionmethods may be piezoresistive, piezoelectric, resonant, optical,magnetic, electromagnetic and the like.

The polysilicon structural layer 661 may also be used to form etch holes598 and 600 in the pressure sensor 504. These are openings in thediaphragm structural component 599 and can be formed in both the fieldregion and the sensor region. The polysilicon structural layer isremoved in the diaphragm structural component so as to provide access tothe sacrificial oxide structural layers (not shown in FIG. 5). In thisexemplary embodiment, the polysilicon structural layer is removed toform the etch holes 598 and 600 in the field region. In anotherembodiment, the etch holes in the polysilicon structural layer 599 canbe formed in the sensor region. These etch holes in the diaphragmstructural component are then sealed using another structural layer toform a sealed cavity that encloses a vacuum.

In the microphone 506, the polysilicon structural layer is used in thefield region 513 and 515 and sensor region 514 for the formation ofstatic and dynamic structural components.

In the field region 513 and 515 of the microphone 506, the polysiliconstructural layer 661 is used to form the anchor or support of themicrophone membrane. The membrane is supported on the nitride structurallayer by the anchor or support components 602 and 607 formed in thefield region. The polysilicon structural layer 661 is also used, in theexemplary embodiment, to connect the membrane to the verticalinterconnect that is used to connect the membrane to an electrode of theinterface circuit that is attached to the other side of the handlelayer. Thus, the polysilicon structural layer 661 is used to form acontact 603 to the vertical interconnect 655. In another embodiment, thestructural layer 661 may be used to form a planar interconnect structurethat is supported on the nitride structural layer 562 and connects thediaphragm to the vertical interconnect 655.

In the sensor region 514 of the microphone 506, the polysiliconstructural layer 661 is used to form the dynamic structural component ofthe membrane. This dynamic structural component of the microphone is themembrane 605 that responds to the sound waves that exert pressure on themembrane. The polysilicon structural layer 661 is used to form themembrane 605 of the membrane that moves under the impinging sound wavesby being supported by an anchor region that contacts the underlyingnitride structural layer in its periphery and then forming a gap fromthe static or reference structural component 12 of the membrane whichencloses a cavity that is exposed to the ambient pressure. Thus, themembrane 605 of the microphone encloses a cavity that is at a pressuresame as the ambient pressure.

The amount of deflection of the microphone membrane is governed bymaterial properties and geometrical dimensions of the microphonemembrane. The deflection is dependent on the thickness of thepolysilicon structural layer 661, the geometric dimensions of themicrophone membrane, the material properties of the polysiliconstructural layer such as modulus of elasticity, Poisson's ratio etc. Themicrophone membrane may have different shapes depending on the designand the application for which the microphone is intended to be used. Themicrophone membrane may be circular, square, rectangular, octagonal etc.in shape. In the exemplary embodiment, the shape of the membrane isassumed to be circular. In this case, the size (radius) is chosen tohave a maximum deflection at the center of the membrane and the range offrequencies to be detected by the microphone.

In the sensor region of the microphone, the polysilicon structural layer661 thus is used to form the membrane, the dynamic structural component605. The microphone in this exemplary embodiment uses capacitancetransduction to convert the sound waves being measured into anequivalent electrical parameter. In this exemplary embodiment, thedynamic structural component which is the membrane is separate by asmall gap from the static structural component or the reference plate orelectrode 586 and 554 formed by the polysilicon structural layer and theactive or device structural layer. Thus, the membrane 605 forms a plateof a capacitance that is capable of movement (deflection) under theinfluence of an applied sound wave. The structural component 586 and 554forms the static or reference plate of the capacitance formed with themembrane. For ease of analysis, the capacitance is considered to be aparallel plate capacitance with the membrane forming one plate orelectrode of the capacitance and the reference or static plate formingthe other plate or electrode of the parallel plate capacitance. Thecapacitance is defined by the formula

$C = \frac{ɛ\; A}{d}$

where ε is the dielectric constant, A is the area of each plate and d isthe gap spacing between the plates. When the dynamic component of themicrophone, which is the membrane, moves down (deflects down towards thereference plate) due to an increase in the ambient pressure applied bythe sound wave, the gap between the diaphragm and the static referenceplate is decreased and the capacitance is increased. The change in thecapacitance is equivalent to the change in the acoustic pressure appliedto the membrane from an equilibrium value. If the pressure applied onthe membrane (which is the dynamic component) is decreased, the membranemoves up (deflects away from the reference plate) and the gap betweenthe diaphragm and the reference plate is increased. The increase in thegap between the diaphragm and the static or reference plate decreasesthe capacitance and the change in capacitance is equivalent to thechange in the pressure applied to the membrane from an equilibriumvalue. Thus, the membrane and the static or reference plate forms acapacitance transducer that converts the incident acoustic or soundwaves into an equivalent capacitance. Other methods of transduction mayalso be used to convert the deflection of the membrane to an equivalentelectrical signal. These other transduction methods may bepiezoresistive, piezoelectric, magnetic, electromagnetic, resonant,optical and the like.

The polysilicon structural layer 661 may also be used to form etch holes604 and 606 in the microphone 506. These are openings in the diaphragmstructural component 605 and can be formed in both the field region andthe sensor region. The polysilicon structural layer is removed in themembrane structural component so as to provide access to the sacrificialoxide structural layers (not shown in FIG. 5B). In this exemplaryembodiment, the polysilicon structural layer is removed to form the etchholes 604 and 606 in the field region. In another embodiment, the etchholes in the polysilicon structural layer 661 can be formed in thesensor region. These etch holes in the diaphragm structural componentenables the membrane to vibrate in response to the incident acoustic orsound waves.

The layer used in 611 is another layer used for the structuralcomponents of the device 500. In this exemplary embodiment, layer usedin 611 is an APCVD oxide. It is an insulator and is deposited in anon-conformal manner. Layer used in 611 is used in the accelerometer502, pressure sensor 504 and microphone 506, for the implementation ofthe static and dynamic structural components of the sensors in both thefield region and the sensor region.

In the accelerometer 502, the layer used in 611 is used in the fieldarea to provide a seal for the etch holes 592 and 594 in the fieldregion and provide mechanical support for the cap structural component611 in the sensor region. In the field region of the accelerometer, thelayer forms a seal over the etch holes so that the atmosphere in thecavity enclosed by the cap structure is fixed and does not allow theexternal atmosphere from affecting the performance of the accelerometer.The non-conformal deposition of the layer ensures that the etch holes592 and 594 are sealed by layer 661, which acts as a plug 610 and 612for the etch holes 592 and 594.

In the sensor area of the accelerometer, the layer forms a continuouslayer 611 over the cap structural component to provide mechanicalsupport to the cap structure 615. By increasing the combined thicknessof the cap structure 593 and 611, the mechanical strength of the cap isincreased so that it does not exhibit deflection due to the ambientpressure applied on the cap structure. Since the mechanical strength ofa plate increases by a cube of its thickness, by increasing thethickness of the layers used for the cap structure, the mechanicalstrength is increased non-linearly. The sealing of the cavity under thecap by the sealing plugs 610 and 612 and the mechanical strength fromthe cap and sealing layers ensures that the cavity under the cap is at afixed volume.

In the pressure sensor 504, the layer used in 611 can be used in thefield and sensor regions for the implementation of the static anddynamic structural components. In the exemplary embodiment shown in FIG.5B, layer 611 is not used in the field and sensor regions of thepressure sensor 504. In other embodiments, the layer 611 may be used forforming a bossed diaphragm to improve the linearity of the pressuresensor.

In the microphone 506, the layer used in 611 can be used in the fieldand sensor regions for the implementation of the static and dynamicstructural components. In the exemplary embodiment shown in FIG. 5B,layer used in 611 is not used in the field and sensor regions of themicrophone 506.

The layer used in 615 is another layer used for the structuralcomponents of the device 500. In this exemplary embodiment, layer usedin 615 is a LPCVD silicon nitride. It is an insulator and is depositedin a conformal manner. Layer used in 615 is used in the accelerometer502, pressure sensor 504 and microphone 506, for the implementation ofthe static and dynamic structural components of the sensors in both thefield region and the sensor region.

In the accelerometer 502, the layer used in 615 is used in the fieldarea to provide a seal for the seal layer 611 in the field region andprovide mechanical support for the cap structural component 593 in thesensor region. In the field region of the accelerometer, the layer formsa seal over the sealing layer 611 so that the atmosphere in the cavityenclosed by the cap structure is fixed and does not allow the externalatmosphere from affecting the performance of the accelerometer. Theconformal deposition of the layer 615 ensures that the etch holes 592and 594 are sealed by layer 615, which acts as a plug for the etchholes. In the field region of accelerometer 502, the layer 615 extendsbeyond the seal layer 611 and provides protection during subsequentfabrication steps of the device 500.

In the sensor area of the accelerometer, the layer 615 forms acontinuous layer over the cap structural component to provide mechanicalsupport to the cap structure 593 and 611. By increasing the combinedthickness of the cap structure 593 and 611, the mechanical strength ofthe cap is increased so that it does not exhibit deflection due to theambient pressure applied on the cap structure. Since the mechanicalstrength of a plate increases by a cube of its thickness, by increasingthe thickness of the layers used for the cap structure, the mechanicalstrength is increased non-linearly.

In the pressure sensor 504, the layer used for 615 can be used in thefield and sensor regions for the implementation of the static anddynamic structural components. In the exemplary embodiment shown in FIG.5, layer used for 615 is not used in the field and sensor regions of thepressure sensor 504. In other embodiments, the layer used for 615 may beused for forming a bossed diaphragm to improve the linearity of thepressure sensor.

In the microphone 506, the layer used for 615 can be used in the fieldand sensor regions for the implementation of the static and dynamicstructural components. In the exemplary embodiment shown in FIG. 5B,layer used for 615 is not used in the field and sensor regions of themicrophone 506.

The layer 620 is another layer used for the structural components of thedevice 500. In this exemplary embodiment, layer 620 is a PECVD Oxidelayer. It is an insulator and is deposited in a non-conformal manner.Layer 620 is used in the accelerometer 502, pressure sensor 504 andmicrophone 506, for the implementation of the static and dynamicstructural components of the sensors in both the field region and thesensor region.

In the accelerometer 502, the layer 620 may be used in the field regionand sensor region for the implementation of the static and dynamicstructural components of the accelerometer. In this exemplaryembodiment, the layer 620 is not used for the implementation of theaccelerometer. In other embodiments, the layer 620 may be left on top ofthe cap structure formed by 593, 611 and 615 to increase the mechanicalstrength of the cap structure. Since the mechanical strength of a plateincreases by a cube of its thickness, by increasing the thickness of thelayers used for the cap structure, the mechanical strength is increasednon-linearly.

In the pressure sensor 504, the layer 620 may be used in the fieldregion and sensor region for the implementation of the static anddynamic structural components of the pressure sensor. In this exemplary,embodiment, the layer 620 is used in the field region of the pressuresensor to form a seal or plug over layer 598 so that the atmosphere inthe cavity enclosed by the diaphragm is fixed. In this exemplaryembodiment, since the layer 620 is a PECVD oxide which is deposited atabout (0.5-5) Torr, the cavity enclosed by the pressure sensor diaphragmis sealed at about (0.5-5) Torr. Thus, structural components 620 and 621form plugs or seals over the etch holes 598 and 600 in the field regionof the pressure sensor diaphragm 599. In other embodiments, layer 620may be used in the sensor region 511 of the pressure sensor to form abossed diaphragm to improve the linearity of the pressure sensor. Sincethe cavity below the diaphragm of the pressure sensor is sealed at avacuum, it is capable of varying in volume due to the deflection of thediaphragm under the pressure applied on the surface of the diaphragm onthe external side of the cavity,

In the microphone 506, the layer 620 may be used in the field region andsensor region for the implementation of the static and dynamicstructural components of the microphone. In this exemplary embodiment,the layer 620 is not used for the implementation of the microphone.

The layer 625 is another layer used for the structural components of thedevice 500. In this exemplary embodiment, layer 625 is a LPCVD SiliconNitride layer. It is an insulator and is deposited in a conformalmanner. Layer 625 is used in the accelerometer 502, pressure sensor 504and microphone 506, for the implementation of the static and dynamicstructural components of the sensors in both the field region and thesensor region.

In the accelerometer 502, the layer 625 may be used in the field regionand sensor region for the implementation of the static and dynamicstructural components of the accelerometer. In this exemplaryembodiment, the layer 625 is not used for the implementation of theaccelerometer. In other embodiments, the layer 625 may be left on top ofthe cap structure formed by 593, 611 and 615 to increase the mechanicalstrength of the cap structure. Since the mechanical strength of a plateincreases by a cube of its thickness, by increasing the thickness of thelayers used for the cap structure, the mechanical strength is increasednon-linearly.

In the pressure sensor 504, the layer 625 may be used in the fieldregion and sensor region for the implementation of the static anddynamic structural components of the pressure sensor. In this exemplary,embodiment, the layer 625 is used in the field region of the pressuresensor to form a seal or plug over layer 620 so that the atmosphere inthe cavity enclosed by the diaphragm is fixed. Thus, structuralcomponents 625 and 626 form plugs or seals over the plugs or seals 620and 621 in the field region of the pressure sensor diaphragm 599. Inother embodiments, layer 625 may be used in the sensor region 511 of thepressure sensor to form a bossed diaphragm to improve the linearity ofthe pressure sensor.

In the microphone 506, the layer 625 may be used in the field region andsensor region for the implementation of the static and dynamicstructural components of the microphone. In this exemplary embodiment,the layer 625 is not used for the implementation of the microphone.

As shown in FIG. 6, the substrate 516 for the implementation of device500 is a SOI (Silicon on Insulator) wafer. The SOI wafer consists of thehandle layer 519 which provides mechanical support for the sensors thatare built in device 500. In one embodiment, the handle layer is composedof monocrystalline silicon and is doped n-type. The buried oxide (BOX)518 is a layer over the handle layer and is used to serve a number ofpurposes in the device 500 such as acting as an anchor, a sacrificiallayer, a motion stop layer and the like. The thickness of the BOX layeris between (0.2-3) microns. The device layer 517 of the SOI wafer iscomposed of monocrystalline silicon and is doped n-type. The handlelayer and the device layer can be any semiconductor material orcombinations of materials such as silicon, monocrystalline silicon,silicon carbide, silicon germanium, gallium arsenide and the like andthe BOX layer can be any insulator such as silicon dioxide, siliconnitride, silicon oxynitride, PSG and the like. In one embodiment, theBOX layer is a silicon dioxide and used as a sacrificial layer.

As illustrated in FIG. 7, a pad oxide layer 680 and a silicon nitridelayer 681 is deposited during the formation of the vertical interconnectstructures for the device 500. In one embodiment, the thickness of thepad oxide is approximately 0.1 microns in thickness and is grown on topof the surface of the device layer 517. In one embodiment, the siliconnitride layer is deposited by LPCVD (Low Pressure Chemical VaporDeposition) and is approximately 0.2 microns in thickness. The pad oxidelayer 680 and the silicon nitride layer 681 are used as etch mask forthe vertical structures formed in subsequent fabrication steps.

As Illustrated in FIG. 8, the pad oxide 680 and silicon nitride layer681 are patterned to form the openings of the vertical interconnects forthe sensors formed in device 500. The pad oxide 680 and silicon nitride681 are coated with a photoresist using spin coating and a patterndefined in the photoresist using a lithography mask. The photoresist isselectively removed over the regions where the vertical interconnectsare formed. The silicon nitride layer and the pad oxide layers are thenremoved by a method of etching. The etching of the silicon nitride layer681 and pad oxide layer 680 can be achieved by using wet etching withchemicals or by RIE (reactive ion etching) or by a combination of wetetching and RIE. In one embodiment, the silicon nitride layer and padoxide layer are etched using RIE. The etching of the silicon nitridelayer 681 and the pad oxide 680 exposes the silicon of the device layer517. The device layer 517 is then etched to define openings for thevertical connect structures. It will be appreciated that any one ofnumerous etching processes may be used. However, in a preferredembodiment, a DRIE (Deep Reactive Ion Etch) is used. This DRIE processallows for trenches to be formed with high aspect ratio. The DRIEprocess is used to remove the silicon in the device layer 517 to thesurface of the BOX (Buried Oxide) layer. The buried oxide layer 518below the openings formed in the device layer is then etched using anyone of a wet etch, dry etch (RIE—reactive ion etching) or a combinationof the two. In a preferred embodiment, the buried oxide layer is etchedusing a RIE. The removal of the oxide in the openings defined for thevertical interconnects is followed by another etching process for thehandle layer 519. The etching of the openings for the verticalinterconnects is achieved using DRIE, in a preferred embodiment. FIG. 8shows device 500 after etching the openings for the verticalinterconnect structures. FIG. 8 shows the openings 682 that are made byetching layer 680 and 681 by RIE, followed by DRIE of the device layer517, RIE of BOX layer 518 and DRIE of the handle layer 519. The shape ofthe openings may be (1-20) microns and the shape of the openings may besquare, round, rectangular, octagonal and the like. In one embodiment,the size of the openings 682 are 6 microns and the shape is round. Thedepth of the openings 682 may range from (5-100) microns. In oneembodiment, the depth of the openings for the vertical interconnects is100 microns.

In FIG. 9, the walls of the trenches 682 are covered by an insulatinglayer to provide isolation from the conductive substrate, (the devicelayer 517 and the handle layer 519) so as to prevent electrical shortingof the vertical interconnects and also to reduce the capacitancecoupling to the conductive substrate. The insulating layer may be ansilicon dioxide, silicon nitride, silicon oxynitride, or a combinationof insulating layers. The thickness of the insulating layer can be(0.5-5) microns. In one embodiment, a silicon oxide layer is used forthe insulating layer. The silicon oxide layer may be grown using thermaloxide, or deposited as LPCVD oxide, LPCVD TEOS, LPCVD LTO, LPCVD HTO,SACVD, so as to form a conformal layer on the sidewalls and bottom ofthe trenches 682. In one embodiment, the silicon oxide layer is formedusing growth of thermal oxide. In FIG. 9, 683 is the conformal oxidelayer for the insulating layer. In one embodiment, the thickness of thesilicon oxide insulating layer is 1 micron.

The refilling of the openings for the vertical interconnects with aconductive layer 684 is shown in FIG. 10. The openings that are linedwith the insulating layer are refilled using a conductive layer usingany one of a deposition process. This conductive layer may be composedof polycrystalline (polysilicon) that is doped, epitaxially depositedsilicon and the like and doped with phosphorus, arsenic, antimony, boronand the like. The thickness of the conductive layer is chosen tocompletely refill the openings for the vertical interconnects after theformation of the insulating liner on the sidewalls. In one embodiment,the conductive layer 684 is formed by depositing LPCVD polysilicon thatis doped in-situ (as-deposited) with phosphorus. In another embodiment,the conductive layer is formed by epitaxial growth of silicon which isdoped in-situ. In another embodiment, the conductive layer is formedwith a metal layer such as tungsten, tantalum and the like. In anotherembodiment, the vertical interconnect module may be completed after thefabrication of the sensors.

As illustrated in FIG. 11, the conductive layer in the top surface ofthe substrate is removed leaving the conductive layer 684 only in therefilled trenches. The removal of the conductive layer is done byetching which can be using RIE (reactive ion etching), wet etching,combination of RIE and wet etching, CMP (chemical mechanical polishing)followed by RIE or wet etching. The conductive layer 684 is removed tobe substantially planar with the top surface of the substrate. In oneembodiment, the conductive layer used to refill the verticalinterconnect trench is a phosphorus doped polysilicon and the layer onthe top surface of the substrate is removed using RIE (reactive ionetching) to form the conductive regions of the vertical interconnects650, 651, 652, 653, 654, 655, 656. In this embodiment, the verticalinterconnect is known as a Thru Silicon Via (TSV). In anotherembodiment, the TSV may contain another conductive layer between theliner insulating layer and the conductive layer to reduce the parasiticcapacitance coupling to the substrate.

After forming the vertical interconnects, the nitride layer 681 and padoxide 680 is removed from the top surface of the substrate (which is thedevice layer of the SOI substrate). FIG. 12 shows the substrate afterthe removal of the nitride layer and pad oxide layer. The nitride layer681 and the pad oxide 680 is removed by RIE (reactive ion etching), wetetching, combination of wet etching and RIE and the like. In oneembodiment, the nitride layer is removed using RIE and the pad oxidelayer is removed using a wet etchant containing Hydrofluoric acid orBuffered Hydrofluoric acid and the like.

As illustrated in FIG. 13, an insulating layer 565 is deposited on thetop surface of the device layer of the substrate 516. This insulatinglayer is meant to provide several functions for the sensors formed indevice 500. In one embodiment, the insulating layer 565 is a LPCVD (lowpressure Chemical Vapor Deposition) silicon nitride layer. In anotherembodiment, the layer 565 is a silicon rich silicon nitride layer thathas low residual stress and higher selectivity to HF based etchchemistry that is used in subsequent processing steps for thefabrication of the sensors in device 500. The thickness of the siliconnitride insulating layer is between (0.2-1) microns. In one embodiment,the thickness of layer 565 is 0.5 microns and is a silicon rich LPCVDsilicon nitride layer. The residual stress of the silicon rich siliconnitride layer is less than 200 MPa tensile stress.

The layer 565 is used in the accelerometer 502, pressure sensor 504 andmicrophone 506 in the sensor region and field region for theimplementation of static and dynamic structural components. The layer565 is patterned using conventional processing (photolithography withmasks, followed by etching, such as reactive ion etching) to form thedifferent structural components of the sensors in device 500.

For each of the vertical interconnects of the sensors formed in device500, the layer 565 is used to protect the insulating layer fromsubsequent processing steps. In one embodiment, the silicon nitridelayer 565 is patterned over the top of each vertical interconnect or TSVover the conductive polysilicon refill layer so as to seal the edges ofthe polysilicon used in the vertical interconnect and not expose thelining oxide of the vertical interconnect to HF based chemistry used insubsequent processing steps.

The layer 565 is patterned so as to define the sensor regions and fieldregions for the accelerometer 502, pressure sensor 504 and microphone506. Thus, in FIG. 14, the silicon nitride layer is patterned to definethe sensor region 508 for the accelerometer 502, sensor region 511 forthe pressure sensor 504 and sensor region 514 for the microphone. In oneembodiment, the layer 565 is removed in the sensor region 508 for theaccelerometer 502, sensor region 511 for the pressure sensor 504 andsensor region 514 for the microphone 506. The openings in the layer 565are 685 in FIG. 14, leaving regions 560, 561, 562 and 563 which are usedin the field regions for the device 500.

FIG. 15 illustrates the fabrication of the device 500 in a further stateof processing. The active or device layer of the substrate is patternedand etched to define the field and sensor regions of the sensors and toform the static and dynamic structural components of the accelerometer502, pressure sensor 504 and microphone 506. The device or active layer517 is patterned to form trenches by using photolithography (photoresistand masks) followed by an etching step such as DRIE (deep reactive ionetching) of the device or active layer. DRIE allows the formation oftrenches which as high aspect ratio (the depth of the trenches arehigher than the width of the openings of the trenches). The patterningprocess forms trenches 670, 671, 672, 673, 674, 675, 676 and 677 whichdefine the static and dynamic structural components in the field andsensor regions for accelerometer 502, pressure sensor 504 and microphone506. The width of the trenches formed by the patterning range from (1-5)microns and the depth of the trenches range from (2-100) microns.

In one embodiment, the width of the trenches is approximately 1.8 to 2.0microns and the vertical sidewall of the trench being approximately 89to 90 degrees with respect to the substrate 516. The DRIE, in oneembodiment, etches down to the BOX (buried oxide) layer 518, which actsas an etch stop layer.

The patterning of the device or active layer is used to define fieldregions and sensor regions for the accelerometer 502, pressure sensor504 and microphone 506 and form static and dynamic structural componentsfor the sensors.

In the accelerometer 502, the patterning of the active or device layerforms the field regions 540, 541 and 547, which support the verticalinterconnects 650, 651 and 652 and provides an anchor or support to theprotective cap structure 598 that is subsequently formed. The trenches670, 671, 572, 673 are used to pattern the active layer in the sensorregion to form the structural components 542, 543, 544, 545, and 546.The active layer structural components 542 and 543 are static componentsformed by patterning the active or device layer by forming trenches 670and 671. Similarly, the patterning of the active layer to definetrenches 672 and 673 forms static structural components 545 and 546 fromthe active layer.

The patterning of the active layer by forming trenches 671 and 672defines the dynamic structural component 544 that is able to respond toan input acceleration. This dynamic structural component 544 representsthe proof mass, suspension spring, fingers, plates and the like that iscapable of responding to an acceleration in a direction parallel to thetop surface of the substrate.

In the pressure sensor 504, the patterning of the active or device layerforms the field regions 547, 548, 549 and 551 which support the verticalinterconnects 653 and 654 and provides anchors or supports 596 and 601for the perimeter of the diaphragm 599 that is subsequently formed. Thetrenches 674 and 675 are used to pattern the device or active layer inthe sensor region to form the structural component 550 that forms astatic or reference electrode for the pressure sensor. The structuralcomponent 550 is a wide plate structure and may be round, square,rectangular and the like to form a fixed plate of a capacitive pressuresensor formed with subsequently defined process steps.

In the microphone 506, the patterning of the active or device layerforms the field regions 551, 552, 553, 554 and 555 which support thevertical interconnects 655 and 656 and provides anchors or supports 602and 607 for the perimeter of the membrane 605 that is subsequentlyformed. The trenches 676 and 677 are used to pattern the device oractive layer in the sensor region to form the structural component 554that forms a static or reference electrode for the microphone. Thestructural component 550 is a wide plate structure and may be round,square, rectangular and the like to form a fixed plate of a capacitivemicrophone formed with subsequently defined process steps. In oneembodiment, the structural component 550 may contain additional trenchesfor improved performance of the microphone to reduce air damping.

In FIG. 15, the device or active layer of the SOI substrate wafer ispatterned to form field regions and sensor regions for the accelerometer502, pressure sensor 504 and microphone 506. It will be evident to thoseskilled in the art that the same layer (device layer or active layer) ispatterned to form static and dynamic structural components for differentsensors that respond to different input stimuli.

As illustrated in FIG. 16, a first release etch is performed to releasethe dynamic structural components of the accelerometer 504, pressuresensor 504 and microphone 506. The release etch is used to remove aportion of the Buried Oxide (BOX) layer below the dynamic structuralcomponents so that they are free to respond to an input stimulus. In oneembodiment, a hydrofluoric acid (HF) wet etch is used to remove theportion of the BOX layer below the dynamic structural components. Otherprocesses such as vapor phase HF etch and gaseous HF etch can also beused. The release etch process is performed to minimize the effect ofstiction in the x, y and z direction between the dynamic and fixed tostatic structural components of the sensors. In the accelerometer 502,in the sensor area, the release etch removes the BOX layer below thedynamic structural component 544. The dynamic structural componentconsists of the proof or seismic mass of the accelerometer, sensefingers, spring suspension, and other electrodes that move under theinfluence of an input acceleration. The release etch also partiallyundercuts the BOX layer below the static structural components to formanchors or supports. Thus, the release etch forms BOX anchor 523 for thefixed or static electrode 522 and BOX anchor 524 for static electrode545. The release etch may also be controlled to form a residual stub ordimple (not shown) below the dynamic structural component to preventstiction between the handle layer of the substrate. The release etchalso undercuts a portion of the BOX layer in the field region to formregions 522 and 525 in the accelerometer 502.

As shown in FIG. 16, in the pressure sensor 504, the release etchundercuts the BOX layer in the static or reference electrode 550 leavingan anchor 529 that connects the static electrode to the handle layer andprevents it from any movement. In addition, the release etch also formsBOX anchor regions 528 and 530 in the field region of the pressuresensor.

In the microphone 506, the release etch undercuts the BOX layer in thestatic or reference electrode 554 leaving an anchor 533 that connectsthe static electrode to the handle layer and prevents it from anymovement. In addition, the release etch also forms BOX anchor regions532 and 534 in the field region of the microphone.

After the first release etch, the trenches formed in the device layer byusing DRIE are refilled by using a first sacrificial layer. The firstsacrificial layer is deposited and patterned over the device 500, asshown in FIG. 17. The first sacrificial layer seals the trenches 670,671, 672, 673, 674, 675, 676 and 677 by covering up the openings in thedevice layer and creates a top planar surface in the device layer 517.The first sacrificial layer may fill the trenches 670, 671, 672, 673,674, 675, 676 and 677 completely or partially depending on the processused to form the first sacrificial layer. In one embodiment, the firstsacrificial layer is formed by using PSG (phosphosilicate glass) and theprocess used for the deposition is PECVD (plasma enhanced Chemical VaporDeposition). In one embodiment, the first sacrificial layer of PSG isdeposited using PECVD to refill the trenches in a non-conformal mannerand then reflowed using a high temperature anneal to seal the trenches670, 671, 672, 673, 674, 675, 676 and 677 and form a planar surface onthe device 500. In one embodiment, the first sacrificial layer of PECVDPSG is annealed in a N2, O2 or combination of the above environment toseal the top of the trenches 670, 671, 672, 673, 674, 675, 676 and 677.The material chosen for the first sacrificial layer is able to withstand high temperature processing and able to be removed easily inanother etch process in subsequent processing, as will be explained inmore detail below.

As illustrated in FIG. 17, the first sacrificial layer is patterned toform openings which expose portion of the nitride insulating layer, thevertical interconnects, anchor regions for the static and dynamiccomponents of the accelerometer 502, pressure sensor 504 and microphone506. The first sacrificial layer may be patterned using a resist layerand photolithography and a dry etch, wet etch or a combination of theabove. The portions of the first sacrificial layer left on the surfaceof the device layer 517 after the patterning is represented by 686 inFIG. 17.

As illustrated in FIG. 18, a structural layer 660 is formed over thedevice 500 after the formation of the openings in the first sacrificiallayer. This layer is used in the field region and sensor region of theaccelerometer 502, pressure sensor 504 and microphone 506 to form staticand dynamic structural components. Any suitable material can be used forthis layer that preferably has a low contact resistance (e.g., dopedpolysilicon with a contact resistance of approximately 10-40Ohms/square), has good adhesion with the substrate in the field regionand sensor region, has low sheet resistance (e.g., doped polysiliconwith a sheet resistance of approximately 10-50 Ohms/square), is notetched during a subsequent release etch, has sufficient mechanicalstrength to from the static and dynamic structural components of thesensors formed in device 500. The material used for this layer also haslow residual stress (less than 200 MPa, tensile or compressive, afterbeing annealed) and is capable of withstanding mechanical shocks andvibration when it is used to form the static and dynamic structuralcomponents of the sensor formed in device 500. In one embodiment, thelayer 660 is formed of LPCVD polysilicon using the following processes.The substrate 516 is first cleaned with a hydrofluoric acid process(diluted) to remove any native oxide from the exposed surface of thesubstrate. Next, approximately 2 microns of polysilicon in-situ dopedwith phosphorus is deposited using LPCVD so that the initial stress isbelow 200 MPa tensile stress. An anneal process is performed in a laterstep to reduce the residual stress in the polysilicon layer 660.

As illustrated in FIG. 18, the layer 660 is patterned to form the staticand dynamic structural components of the MIMS device 500. In oneembodiment, the layer 660 is formed of polysilicon which is patternedusing a resist layer and lithography followed by an etch process whichmay be a dry etch, wet etch or a combination of dry etch and wet etch.The patterned polysilicon forms static and dynamic structural componentsof the accelerometer 502, pressure sensor 504 and microphone 506 for theMIMS device 500. In the accelerometer 502, the layer 12 is patterned toform the bridge 571 that connects the static electrode 522 using anchorregions 570 and 572 and connected to the vertical interconnect 651. Thelayer also a suspension spring 574 that is connected to the dynamicstructural component 544 with an anchor 573 at one end and to anotheranchor 576 using a bridge 575 and connected to the vertical interconnect652. In the pressure sensor 504, the layer 660 is patterned to form thebridge 578 that connects the static or reference electrode 580 of thepressure sensor 504 with the vertical interconnect 654 using anchor 577.The reference plate or electrode 580 is connected to the static devicecomponent 550 with anchors 579, 581 and 582. In the microphone, thelayer 660 is patterned to form the bridge 584 that connects the staticor reference electrode 586 of the microphone 506 with the verticalinterconnect 656 using anchor 583. The reference plate or electrode 586is connected to the static device component 554 with anchors 585, 587and 588.

After forming the static and dynamic structural components using layer660, a second sacrificial layer is formed over the MIMS device 500 andpatterned as illustrated in FIG. 20. The second sacrificial layer isused in the sensors in device 500. In one embodiment, the secondsacrificial layer is formed by PSG (phosphosilicate glass) using PECVD,LPCVD, APCVD, CVD, SACVD, PVD, and the like and combinations of theabove. In one embodiment, the second sacrificial layer is formed by PSGand is approximately 1-3 microns in thickness. In one embodiment, thesecond sacrificial layer of PSG is densified by annealing at atemperature of (950-1050) degree Celsius. The second sacrificial layeris patterned using resist and photolithography and etched using wetetching by HF, BHF, dry etch or a combination of wet and dry etch. Inone embodiment, the second sacrificial layer of PSG is patterned using awet etch using HF.

In the accelerometer 502, the second sacrificial layer component 687 isused in the sensor region 508 to define the spacing of the accelerometerto the subsequently formed cap layer. The second sacrificial layer isremoved in the field region to expose underlying layers of nitride, thevertical interconnects and the like.

In the pressure sensor 504, the second sacrificial layer component 687is used in the sensor region 511 to define the spacing of the staticelectrode 580 from the subsequently formed diaphragm. The secondsacrificial layer is removed in the field region to expose underlyinglayers of nitride, the vertical interconnects and the like.

In the microphone 506, the second sacrificial layer component 687 isused in the sensor region 514 to define the spacing of the staticelectrode 586 from the subsequently formed membrane. The secondsacrificial layer is removed in the field region to expose underlyinglayers of nitride, the vertical interconnects and the like.

After the patterning of the second sacrificial layer, a structural layer661 is formed over the MIMS device 500 and the second sacrificial layeras shown in FIG. 21. The structural layer 661 is used in the fieldregion and sensor region of the accelerometer 502, pressure sensor 504and microphone 506 to form static and dynamic structural components. Anysuitable material can be used for this layer that preferably has a lowcontact resistance (e.g., doped polysilicon with a contact resistance ofapproximately 10-40 Ohms/square), has good adhesion with the substratein the field region and sensor region, has low sheet resistance (e.g.,doped polysilicon with a sheet resistance of approximately 10-50Ohms/square), is not etched during a subsequent release etch, hassufficient mechanical strength to from the static and dynamic structuralcomponents of the sensors formed in device 500. The material used forthis layer also has low residual stress (less than 200 MPa, tensile orcompressive, after being annealed) and is capable of withstandingmechanical shocks and vibration when it is used to form the static anddynamic structural components of the sensor formed in device 500. Thethickness of this layer 661 is approximately 1-4 microns. In oneembodiment, the layer 661 is formed of LPCVD polysilicon using thefollowing processes. The substrate 516 is first cleaned with ahydrofluoric acid process (diluted) to remove any native oxide from theexposed surface of the substrate. Next, approximately 2 microns ofpolysilicon in-situ doped with phosphorus is deposited using LPCVD sothat the initial stress is below 200 MPa tensile stress. An annealprocess is performed in a later step to reduce the residual stress inthe polysilicon layer 661.

As illustrated in FIG. 22, the layer 661 is patterned to form the staticand dynamic structural components of the MIMS device 500. In oneembodiment, the layer 661 is formed of polysilicon which is patternedusing a resist layer and lithography followed by an etch process whichmay be a dry etch, wet etch or a combination of dry etch and wet etch.The patterned polysilicon layer forms static and dynamic structuralcomponents of the accelerometer 502, pressure sensor 504 and microphone506 for the MIMS device 500. In the accelerometer 502, the layer 661 ispatterned to form a protective cap structure 593 which is used toprotect the static and dynamic structural components of theaccelerometer from the effects of processing after the device 500 iscompleted. These processes can include wafer thinning, assembly andpackaging. The protective cap structure 593 is anchored to the substrateby 590 and 595 and connected to the vertical interconnect 650 by 591.The layer 661 is also patterned to form etch holes (openings) 592 and594 to allow the chemicals used in the release etch to reach the secondsacrificial layer, first sacrificial layer and the BOX layer so that atleast portions of these layers are removed to release the MIMS device500. The layer 661 may also be used to form pillars or walls (not shownin FIG. 22) supported on the static structural components to improve themechanical strength of the cap structure 593.

As illustrated in FIG. 22, in the pressure sensor 504, the polysiliconlayer 661 is patterned to form the pressure sensitive diaphragm 599which is separated from the static or reference plate or electrode 580by the thickness of the second sacrificial layer. The diaphragm 599formed by the polysilicon layer 661 is supported in the periphery by theanchor regions 596 and 601 and connected to the vertical interconnect653 by connection region 597. The shape of the diaphragm 599 may beround, square, rectangular, octagonal and the like and may be 50-500microns in size.

The layer 661 is also patterned to form etch holes (openings) 598 and600 to allow the chemicals used in the release etch to reach the secondsacrificial layer, first sacrificial layer and the BOX layer so that atleast portions of these layers are removed to release the MIMS device500.

As illustrated in FIG. 22, in the microphone 506, the polysilicon layer661 is patterned to form the sound sensitive membrane 605 which isseparated from the static or reference plate or electrode 586 by thethickness of the second sacrificial layer. The membrane 605 formed bythe polysilicon layer 661 is supported in the periphery by the anchorregions 602 and 607 and connected to the vertical interconnect 655 byconnection region 603. The shape of the membrane 605 may be round,square, rectangular, octagonal and the like and may be 50-500 microns insize.

The layer 661 is also patterned to form etch holes (openings) 604 and606 to allow the chemicals used in the release etch to reach the secondsacrificial layer, first sacrificial layer and the BOX layer so that atleast portions of these layers are removed to release the MIMS device500.

The second release etch is performed in the MIMS device 500 to releasethe dynamic structural components by removing the second sacrificiallayer, the first sacrificial layer and a portion of the BOX layer sothat the dynamic structural components are able to move under an inputstimulus as shown in FIG. 23. The release etch chemistry chosenpreferably minimizes the etching of the anchors 522, 523, 524, 528, 529,532, 533, and 534 for the MIMS device 500. The release etch preferablyhas no stiction in the x, y and z directions between the dynamic andstatic structural components of the sensors in MIMS device 500. It maybe desirable to perform an overetch to account for variations across awafer to ensure complete removal of the second sacrificial layer, thefirst sacrificial layer and a portion of the BOX sacrificial layer. Thesecond release etch removes the second sacrificial layer and firstsecond sacrificial layer and a portion of the BOX layer in theaccelerometer 502 so that the dynamic structural components 544 and 574are suspended and free to move under an input acceleration. The dynamicstructural component consists of the proof or seismic mass, fingers, andsuspension spring. In the pressure sensor 504, the second release etchremoves the second sacrificial layer, first sacrificial layer and aportion of the BOX layer so that the dynamic structural component 599 isfree to move under an input pressure. The dynamic structural component599 is the pressure sensitive diaphragm. In the microphone 506, thesecond release etch removes the second sacrificial layer, firstsacrificial layer and a portion of the BOX layer so that the dynamicstructural component 605 is free to move under an input sound wave. Thedynamic structural component 605 is the sound sensitive membrane.

In one embodiment, a hydrofluoric acid (HF) wet etch is used to removethe second sacrificial layer, first sacrificial layer and a portion ofthe BOX layer below the dynamic structural components. Other processessuch as vapor phase HF etch and gaseous HF etch can also be used. Therelease etch process is performed to minimize the effect of stiction inthe x, y and z direction between the dynamic and fixed to staticstructural components of the sensors.

In another embodiment, the first release etch is not performed and therelease etch is performed in a single step to remove the secondsacrificial layer, first sacrificial layer and a portion of the BOXlayer below the dynamic structural components.

After the release etch, the dynamic structural components of the sensorsin MIMS device 500 are now free to move. However, the holes 592 and 594in the accelerometer cap 593, holes 598 and 600 in pressure sensordiaphragm 599 and holes 604 and 606 in the microphone membrane 605 canallow particles and moisture to enter into the cavity below theaccelerometer 593, diaphragm 599 and membrane 605 to negatively affectthe performance of the sensors in device 500.

In one embodiment, the holes 592 and 594 in the accelerometer cap 593are sealed using a first sealing layer forming sealing component 611.The layer forming sealing component 611 seals the etch holes 592 and 594in a nonconformal manner so that the holes are sealed by plugs 610 and612. In one embodiment, the sealing layer is an oxide deposited by APCVD(Atmospheric Pressure Chemical Vapor Deposition), which seals the cavitybelow the cap structure 593 at approximately one atmosphere of pressure.In another embodiment, the sealing component 611 and plugs 610 and 612are formed by spin-on glass. The thickness of the layer forming 611 isdependent on the size of the etch holes and the height and thickness ofthe cap layer 593. The sealing layer is patterned using resist andphotolithography followed by an etch which may be a wet etch, dry etchor a combination. In FIG. 24, the sealing layer is an APCVD oxide thatis patterned to form sealing component 611, plugs 610 and 612 over theaccelerometer cap 593 and also leaving the sealing layer over thepressure sensor diaphragm 599 and over the microphone membrane 605.

To improve the reliability of the sealing of the cap structure 593 ofthe accelerometer 502, a second sealing layer is deposited andpatterned. In one embodiment, this second sealing layer is formed bydepositing a LPCVD silicon nitride layer that is patterned using resistand photolithography followed by an etch which may be a dry etch, wetetch or a combination. In one embodiment, the sealing layer is a LPCVDsilicon nitride layer of approximately 0.3 microns in thickness andpatterned to form sealing component 615 over the accelerometer withfirst sealing component 611 formed over cap structure 593. The secondsealing layer is etched over the pressure sensor 504 and the microphone506. This is followed by an etch which removes the first sealing layerabove the pressure sensor 504 and microphone 506. As illustrated in FIG.25, the accelerometer cap 593 is sealed using a first sealing layercomponent 611 followed by a second sealing layer component 615 while thepressure sensor 504 and microphone 506 are not sealed at this step. InFIG. 25, the sealing of the accelerometer cap using the first and secondsealing layers ensures that the cavity below the cap structure 593 aresealed at substantially a fixed volume since the cap structure 593 isdesigned to stay rigid with high mechanical strength. This ensures thatthe dynamic structural components of the accelerometer 502 are protectedfrom the environment and free to move under the applied accelerationthat it is measuring.

After completing the formation of the accelerometer 502, the cavitybelow the diaphragm 599 of the pressure sensor 504 is sealed using athird sealing layer 664 and a fourth sealing layer 665 as illustrated inFIG. 26. The cavity below the pressure sensor diaphragm 599 is sealedusing the third sealing layer 664 which is deposited in a vacuum. In oneembodiment, the sealing layer 664 for the pressure sensor is a PECVDoxide which is deposited in a vacuum of 1-4 Torr and plugs the etchholes 598 and 600 in a non-conformal manner. In another embodiment, thesealing layer 664 is a PECVD PSG. In yet another embodiment, the sealinglayer is a sputtered oxide. Whatever the sealing layer 664 used, it isdeposited in a vacuum and in a non-conformal manner so as not toencroach into the cavity below the diaphragm. The thickness of thesealing layer 664 is dependent on the size of the etch holes 598 and 600and the height and thickness of the diaphragm 599. To improve thereliability of the sealing of the etch holes 598 and 600 by the thirdsealing layer 664, a fourth sealing layer 665 is deposited over thethird sealing layer 664. In one embodiment, the fourth sealing is aLPCVD Nitride with an approximate thickness of 0.3 microns.

The third sealing layer and fourth sealing layer are patterned usingresist and photolithography followed by the etch of the fourth sealinglayer and third sealing layer which may be a dry etch, wet etch, or acombination. In one embodiment, the third and fourth sealing layers areetched using dry etch forming plug comprising 620 and 625 over etch hole598 and plug comprising 621 and 626 over etch hole 600. In oneembodiment, the third sealing layer 12 and fourth sealing layer areremoved over accelerometer 502. In another embodiment, the third sealinglayer 664 and fourth sealing layer 665 remain over accelerometer 502 toimprove the mechanical strength of the cap. The sealing of the cavitybelow the diaphragm 599 in a vacuum by using plugs comprising 620 and625 over etch hole 598 and plug comprising 621 and 626 over etch hole600 ensures that the diaphragm 599 is able to respond to an externalpressure by deflecting under the applied pressure. Since the gap betweenthe diaphragm (which is a dynamic structural component) changes with thereference electrode 580 (which is the static structural component), thecapacitance changes and the change in the pressure is measured as achange in capacitance. In the microphone 506, the removal of the thirdsealing layer 664 and fourth sealing layer 665 ensures that the membrane605 is able to respond to a sound wave and cause a gap change with thereference electrode 586 which causes a change in the capacitance and theinput sound wave is measured as a change in capacitance.

After the completion of the MIMS device 500, the substrate 516 isthinned to expose the vertical interconnects that are used to connectthe electrodes of the sensors in the MIMS device 500 to an interfacecircuit. In one embodiment, the handle layer is thinned using mechanicalremoval (coarse grind, fine grind), dry etching, wet etching and acombination to expose the vertical interconnects on the back side of thesubstrate 515. This is illustrated in FIG. 28, when the backsidethinning process exposes the conductors in the vertical interconnects650, 651, 652, 653, 654, 655 and 656.

The thinned wafer is then connected to an interface circuit 668 by usinga bond process that produces a low resistance connection between theelectrodes of the sensors in MIMS device 500 to a correspondingconnection in the interface circuit 668. This is illustrated in FIG. 29,where the substrate 516 containing the MIMS device 500 is connected tothe interface circuit 668 with bond connections 667. In one embodiment,the bond connections are formed using Gold/Tin eutectic solder. Othersolder connections may be used in other embodiments such as Tin/Copper,Tin/Silver and the like. The connection of the MIMS device 500 to theinterface circuit may be done at the die to die, or die to wafer orwafer to wafer. In one embodiment, the attachment of the MIMS device 500die to the interface circuit is performed at the die to die level.

FIG. 30 illustrates a simplified cross-sectional view of an exampleembodiment 950 for MIMS device 500 in which the layers 664 and 665 areused in the accelerometer 502 over the cap 593 to increase themechanical stiffness of the protective cap since the layers used for theimplementation are 593, 611, 615, 690 and 691. Since the mechanicalstiffness of the cap increase as the cubic power of the thickness, theincrease of the cap structure to include 690 and 691 increases thestiffness. The same layers 664 and 665 are used for sealing the etchholes 598 and 600 of the diaphragm 599 of the pressure sensor 504. Thus,layers 664 and 665 are used in the accelerometer 502 to increase themechanical stiffness of the cap structure and for sealing of the etchholes 598 and 600 for the diaphragm 599 of the pressure sensor 504.

FIG. 31 illustrates a simplified cross-sectional view of an exampleembodiment 955 for MIMS device 500 in which the layers 664 and 665 areused in the accelerometer 502 over the cap to increase the mechanicalstiffness of the cap as well as in the pressure sensor 504 both forsealing the cavity below the diaphragm but also to improve theperformance of the pressure sensor. In this implementation, the layers664 and 665 are used over the cap of the accelerometer to increase themechanical strength as shown in FIG. 30. In the pressure sensor 504, thelayers 664 and 665 are used for sealing the etch holes 598 and 600 toform the sealed cavity below the diaphragm 599. In the alternateembodiment 955, the layers 664 and 665 are used for forming a boss orrigid structure on top of the pressure sensitive diaphragm. Thus, theboss or rigid center structure is formed by structural components 692and 693 using layers 664 and 665. The boss formed by structuralcomponents 692 and 693 improves the linearity of the pressure sensorresponse to an applied pressure so that the capacitance formed by therigid boss of the pressure sensor diaphragm 599 and the static orreference electrode 580 shows a more linear response. Thus, in theimplementation of FIG. 31, the layers 664 and 665 are used in theaccelerometer 502 to increase the stiffness of the static component(cap) 593 and in the pressure sensor 504 to seal the etch holes 598 and600 to form a vacuum below the diaphragm and in the dynamic component(the pressure sensitive diaphragm) 599 to form a boss or rigid center toimprove the linearity of the pressure sensor 504.

FIG. 32 illustrates a simplified cross-sectional view of an exampleembodiment 960 for MIMS device 500 in which the layers 662, 663, 664 and665 are used in the accelerometer 502 as well in the pressure sensor504. In this implementation, layers 662 and 663 are used in theaccelerometer 502 to seal the etch holes 592 and 594 so as to seal thecavity under the cap structural component 593. These layers 662 and 663are formed over the cap structural component to impart rigidity andprevent any motion of the cap structure. In the pressure sensor 504, thelayers 662 and 663 are used to form components 694 and 695 of a boss orrigid structure over the dynamic structural component (diaphragm 599) toimprove the linearity of the pressure sensor. Thus, layers 662 and 663are used in the accelerometer 502 to form static or rigid structuralcomponents 611 and 615 over the cap structural component 593 and in thepressure sensor 504, to form dynamic structural components 694 and 695of the boss or rigid center of the dynamic structural component(diaphragm 599).

Layers 664 and 665 are used for sealing the etch holes 598 and 600 ofthe pressure sensor diaphragm 599 and also for forming components 696and 697 of the boss or rigid center over the dynamic structuralcomponent (diaphragm 599) to improve the linearity of the pressuresensor. In the accelerometer 502, the layers 664 and 665 are used toform rigid or static structural components to improve the rigidity ofthe cap 593 of the accelerometer 502. Thus, layers 664 and 665 are usedin the accelerometer 502 to form static or rigid structural components690 and 691 over the cap structural component 593 and in the pressuresensor 504, to form dynamic structural components 696 and 697 of theboss or rigid center of the dynamic structural component (diaphragm 599)and static structural components (plugs 620, 621 625 and 626 over etchholes 598 and 600.

FIG. 33 illustrates a simplified cross-sectional view of an exampleembodiment 965 where layer 660 is used for the implementation of staticand dynamic structural components in the accelerometer 502, pressuresensor 504 and microphone 506 while the accelerometer 502 and microphone506 is formed as in MIMS device 500.

For the accelerometer 502, the device layer 517 is used for the staticand dynamic structural components 543, 544 and 545. The device layeralso supports the protective cap 593 formed by layers 661, 662 and 663.

For the pressure sensor 504, the device layer 517 is used as the staticor reference electrode 714 and connected to the vertical interconnect715. The device layer 517 is also used to support the diaphragm formedby layer 660. The reference electrode 714 is defined by etching trenches713 and 717.

For the microphone 506, the device layer 517 is used for the static orreference electrode 554 for the microphone and connected to verticalinterconnect 656.

The polysilicon layer 660 is used in the accelerometer 502 for theformation of the static and dynamic structural components of theaccelerometer.

The polysilicon layer 660 is used in the pressure sensor 504 for theformation of the pressure sensitive diaphragm 706 that is a dynamicstructural component responding to the pressure applied to the diaphragmand separated from the static or reference electrode formed by devicelayer component 714 by gap 707. In this implementation, the poly layeris used to form a diaphragm that is suspended above the static electrode714 formed by the device layer 517 and supported on the edges by anchor701 and 711 and connected to the vertical interconnect 715 by contactregion 702. The etch holes 703 and 708 are used to remove thesacrificial layer between the diaphragm 706 and the static electrode714. These etch holes 703 and 708 are sealed using layers 664 and 665 toform plugs comprising 704 and 705 and 709 and 710 so that the cavitybelow the diaphragm (dynamic structural component) formed by layer 660is at a vacuum and therefore able to respond to the pressure applied todiaphragm 706. In this implementation, the layer 660 is used for thedynamic structural component (diaphragm) 706 of the pressure sensor.

The polysilicon layer 660 is used in the microphone 506 to form thestatic or reference electrode 586 for the capacitive microphone whichuses the polysilicon layer 661 to form the sound sensitive membrane.

Thus, in the implementation of the device 965, the device layer 517 isused as the static and dynamic components of the accelerometer, thereference electrode of the pressure sensor and a component of thereference electrode for the microphone. The polysilicon layer 660 isused for the formation of static and dynamic components of theaccelerometer, the dynamic structural component (diaphragm) of thepressure sensor and a component of the reference electrode for themicrophone.

FIG. 34 illustrates a simplified cross-sectional view of an embodiment970 for MIMS device 965 where the polysilicon layer 660 is used in theaccelerometer and pressure sensor but removed in the microphone. In thisimplementation, the polysilicon layer is removed in the microphone sothat the device layer 517 is used as the static or reference electrodeand the polysilicon layer 661 is used to form the sound sensitivemembrane. The static or reference electrode 720 is formed by etchingtrenches 719 and 723 and is anchored by BOX 722. The electrode 720 isconnected to the vertical interconnect 721. By removing the poly layer660, the gap 718 between the dynamic structural component (soundsensitive membrane) 605 is enabled to deflect over a larger distance andthis results in the increase of the dynamic range of the microphone.

FIG. 35 illustrates a simplified cross-sectional view of an exampleembodiment 975 for MIMS device 970 where the polysilicon layer 661 isused in the pressure sensor to form a boss or rigid center 724 for adynamic structural component (diaphragm) 706 formed by the polysiliconlayer 660. The other layers used for the boss or rigid center includelayers 662, 663, 664 and 665 forming components 725, 726, 727 and 728 ofthe boss or rigid structure to improve the linearity of the deflectionof the diaphragm 706.

FIG. 36 illustrates a simplified cross-sectional view of an exampleembodiment 980 for MIMS device 975 where the layers 517 and 660 are usedto implement an acceleration sensor that responds to acceleration in thez-axis (in a direction perpendicular to the surface of the substrate. Inthis implementation, device layer 517 is used to form structuralelements 743 and 747 that are static being anchored to the handle layerby the buried oxide anchors 744 and 746. The device layer 517 is alsoused to form dynamic structural components 745, 748 and 749 which formthe proof mass (that moves under the inertial force—in this case,acceleration), the sensing plate and other dynamic components. Thedynamic structural components are free to move vertically since theburied oxide components below them are removed. Dynamic structuralcomponent 745 represents a sensing plate, while 748 and 749 representsthe proof mass. The static structural component 743 is connected to thevertical connect 742.

The poly layer 660 is used to form static and dynamic structuralcomponents of the vertical axis accelerometer. In this implementation,the structural component 733 forms a static or reference plate, beinganchored to the handle layer by anchor region 730 and 734. The static orreference plate is also connected to the vertical interconnect 742 bybridge interconnect 731. The poly layer 660 is used in the dynamicstructural component 748 to form a suspension spring 738 for the proofmass formed by 748 and 749 connected to an anchor 740 which is alsoconnected to the vertical interconnect 750 by a bridge 739.

When the dynamic components of the accelerometer 745, 748 and 749 aresubjected to an acceleration in the direction perpendicular to thesurface of the substrate, the proof mass being suspended by the spring738 moves towards the fixed or reference plate formed 733 by thepolysilicon layer 660. This movement of the dynamic structuralcomponents also causes the sensing plate 745 to move towards the staticor reference plate 733 formed by the poly layer 660. This movement maybe linear or torsional depending on the design of the suspension spring738 formed by polysilicon layer 660. Since the gap between the dynamicstructural component (sensing plate) 745 formed by the device layer andthe static structural component (reference plate or electrode) 733 ischanged, the capacitance is changed in proportion to the inputacceleration. More than one pair of plates can be formed for the z-axisaccelerometer to provide differential measurements of the inputacceleration.

The accelerometer in FIG. 36 thus uses the device layer 517 to formstatic and dynamic structural components for the z-axis accelerometer,and uses polysilicon layer 660 to form the static reference plate andthe spring suspension for the static and dynamic structural componentsof the z-axis accelerometer. Thus, it is evident to those skilled in theart that the structural layers used in MIMS device 980 can be used toform both lateral and z-axis accelerometers.

FIG. 37 shows a simplified cross-sectional view of a MIMS device 1000that consists of multiple devices that are formed on the same substrate,using the same layers used in FIG. 5B for implementation of MIMS device500 and the principle of parallel design. The device 1000 also uses someadditional layers for implementation of multiple sensors on the samesubstrate with added capability. Thus, in this embodiment, device 1000consists of a magnetic sensor 1002, infra-red sensor 1004, force sensor1006 and humidity sensor 1008.

Device 1000 is formed on a substrate comprising a handle layer 819,buried oxide layer 818 and device layer 817. The handle layer 819 isused to provide mechanical support for the sensor 1002, 1004, 1006 and1008. In this implementation, the buried oxide layer 818 is used to formanchors 820 and 821 for the static structural components 840 and 842 forthe magnetic sensor, and is removed below the dynamic structuralcomponent 841. In the infra-red sensor 1004, the buried oxide layer isused to form an anchor 822 for the static component 843. In the forcesensor 1006, the buried oxide layer is used to form an anchor 823 forthe static or reference component 844. In the humidity sensor 1008, theburied oxide layer is used to form an anchor 824 for the static orreference component 845.

The device layer 817 is used for device 1000 for the implementation ofstatic and dynamic components of the magnetic sensor 1002, infra-redsensor 1004, force sensor 1006 and humidity sensor 1008.

In the magnetic sensor 1002, device layer 817 is used for the staticstructural components 840 and 842, which acts as reference electrodesfor capacitances using gaps 871 and 872 that are formed with the dynamiccomponent 841 which is suspended by a suspension spring 862. When anelectrical current is passed through the dynamic component 841, itdeflects under the influence of an ambient magnetic field due to theLorenz force. This deflection of the dynamic structural component 841changes the gaps 871 and 872 which change the capacitances, and thechange in capacitance from a reference position is a measure of themagnetic field. A fixed magnet may also be used to establish the initialreference position of the dynamic structural component 841 with a knownelectrical current.

In the infra-red sensor 1004, the device layer 817 is used to form astatic structural component 843 that supports a reference heater for theinfra-red sensor. The static structural component 843 is supported bythe buried oxide anchor 822.

In the force sensor 1006, the device layer 817 is used to form a staticstructural component 844 that supports a reference electrode for theforce sensor. The static structural component 844 is supported by theburied oxide anchor 823.

In the humidity sensor 1008, the device layer 817 is used to form astatic structural component 845 that supports a reference heater for thehumidity sensor. The static structural component 845 is supported by theburied oxide anchor 824.

In the device MIMS 1000, the layer 815 is an isolation layer to provideelectrical isolation between different static and dynamic componentsthat are at different electrical potentials for the magnetic sensor1002, infra-red sensor 1004, force sensor 1006 and humidity sensor 1008.

In the device 1000, the polysilicon layer 660 used in MIMS device 500 isa structural layer used for the static and dynamic structural componentsof the magnetic sensor 1002, infra-red sensor 1004, force sensor 1006and humidity sensor 1008. The polysilicon layer 660 is a LPCVDpolycrystalline silicon or polysilicon layer. Layer represented by 660is a conductive layer.

In the magnetic sensor 1002, the polysilicon layer 660 is used to form abridge or interconnect 860 to connect the static structural component861 to the vertical interconnect 915. Layer 660 is also used to form aplate structure 861 to act as a reference or static electrode for themagnetic sensor 1002. The layer 660 is used to form the suspensionspring 862 and a bridge connection 863 to connect the dynamic structuralcomponent 841 to and also connect it to an anchor which is connected tothe vertical interconnect 915. The suspension spring 862 also enablesthe injection of the device current to interact with the magnetic field.

In the infra-red sensor 1004, the layer 660 is used to form a staticstructural component that is connected to the vertical interconnect 915by a bridge interconnect 864 and also forms a suspended heater 865 thatis used as a reference for the infra-red sensor.

In the force sensor 1006, the layer 660 is used to form a staticstructural component that is connected to the vertical interconnect 915by a bridge interconnect 866 and also to form a static plate orreference electrode 867 for the capacitance force sensor.

In the humidity sensor 1008, the layer 660 is used to form a staticstructural component that is connected to the vertical interconnect 915by a bridge interconnect 868 and also forms a suspended heater 869.

In the device 1000, the layer 661 is the structural layer in MIMS device500 and used for the static and dynamic structural components of themagnetic sensor 1002, infra-red sensor 1004, force sensor 1006 andhumidity sensor 1008. Layer 661 is a LPCVD polycrystalline silicon orpolysilicon layer used in device 500. Layer 661 is a conductive layer.

In the magnetic sensor 1002, the layer 661 is used to form a protectivecap over the static and dynamic structural components. Layer 661 is usedto form the static protective cap structure 880 which protects thestatic and dynamic structural components of the magnetic sensor and isconnected to the vertical interconnect 915. The layer 661 may also beused to form pillars, post, walls to increase the mechanical stiffnessof the protective cap 880. The layer 661 may also be used to form etchholes that are subsequently sealed to enclose the cavity below the capstructure 880 in a fixed atmosphere.

In the infra-red sensor 1004, the layer 661 is used to form the elementsof the infra-red sensor. Thus, 881 and 882 are used to form a suspendedstatic structure that has two junctions to form a thermopile. Bysuspending the structural components 881 and 882, the thermal resistanceis improved and the thermal isolation increased. The static structuralcomponent 881 is connected to the vertical interconnect 915.

In the force sensor 1006, the layer 661 is used to form a dynamicstructural component that responds to the applied force. The dynamicstructural component 883 is a plate or diaphragm is suspended above thereference plate or electrode formed by 867. The diaphragm 883 issupported by anchor structures in the periphery and connected to thevertical interconnect 915. The diaphragm moves downwards when a force isapplied so that the gap between the diaphragm 883 and the referenceelectrode 867 is reduced and the capacitance increases. The change incapacitance is a measure of the force applied on 883.

In the humidity sensor 1008, the layer 661 is used to form a staticstructural component of the humidity sensor. The static structuralcomponent 884 is used to form a suspended reference plate or electrodefor the capacitive humidity sensor. The reference plate 884 is connectedto the vertical interconnect 915.

The layer 664 used in MIMS device 500 is a layer used for the static anddynamic structural components of device 1000. Layer 664 is an insulatinglayer. In the magnetic sensor 1002, the layer 664 is used to seal theetch holes in the structural component 880 so that the cavity below issealed at a vacuum. The component 885 combines with cap structure 880 toprotect the static and dynamic structural components of the magneticsensor from the external atmosphere while still coupling with themagnetic fields. In the infra-red sensor 1004, the layer 664 is used toseal the etch holes in the structural components 881 and 882 using plugs886 and 887. In the force sensor 1006, the layer 664 is used to seal theetch holes in the structural component 883 so that the cavity below issealed at a vacuum. The components 888 and 889 seals the etch holes inthe cap structure 883 to protect the static structural components of theforce sensor from the external atmosphere. In the humidity sensor 1008,the layer 664 is used to seal the etch holes in the structural component884 so that the cavity below is sealed at a vacuum. The components 890and 891 seals the etch holes in the cap structure 884 to protect thestatic structural components of the humidity sensor from the externalatmosphere.

In the device 1000, the layer 665 used in MIMS device 500 is anotherlayer used for the static and dynamic structural components. Layer 665is an insulating layer.

In the magnetic sensor 1002, the layer 665 is used to protect the staticand dynamic structural components of the sensor. The component 895combines with cap structure 880 and 885 to protect the static anddynamic structural components of the magnetic sensor from the externalatmosphere while still coupling with the magnetic fields.

In the infra-red sensor 1004, the layer 665 to is used to seal the etchholes in the structural components 881 and 882. The layer 665 is used toform plugs 896 and 897 above the sealing plugs 886 and 887.

In the force sensor 1006, the layer 665 is used to seal the etch holesin the structural component 883 so that the cavity below is sealed at avacuum. The components 898 and 899 combines with 888 and 889 and capstructure 883 to protect the static structural components of the forcesensor from the external atmosphere.

In the humidity sensor 1008, the layer 665 is used to seal the etchholes in the structural component 884 so that the cavity below is sealedat a vacuum. The components 900 and 901 combines with component 890 and891 and with cap structure 884 to protect the static structuralcomponents of the humidity sensor from the external atmosphere.

In the implementation of the MIMS device 1000, the layers used in MIMS500 are used. In addition to these layers, some additional layers areused to implement additional sensors.

Layer 905 is an additional layer used for the implementation of thehumidity sensor 1008. The layer 905 is a layer used in device 1000 inaddition to the layers used in device 500, to enable the formation ofthe humidity sensor. Layer 905 is a polyimide layer that is sensitive tothe change in the humidity and which changes its dielectric constantwith the ambient humidity. Structural component 905 is a polyimide layerthat changes its dielectric constant with the ambient humidity in thehumidity sensor 1008.

Another layer used in the implementation of sensors in MIMS device 1000is a metallic layer. The layer is a metallic layer such as tantalum,platinum, titanium and the like which is used for the implementation ofthe infra-red sensor 1004 and the humidity sensor 1008.

In the infra-red sensor 1004, the metallic layer is used to form thestructural component 906 and 907 which forms the junctions with thelayer 661, which is a doped polysilicon layer. The metallic layercomponents 906 and 907 formed by the metallic layer is chosen to have alarge difference in Seebeck coefficients so that the voltage differencebetween the two junctions is large and changes proportionally with theinfra-red radiation that is being measured.

In the humidity sensor 1008, the metallic layer is used to form thestatic structural components that form the upper plate or electrode 908and 909 of the capacitance that is formed with the structural component884 as the lower plate or electrode and the polyimide humidity sensitivedielectric 905 between 908 and 909 and 884. The components 908 and 909may be used in the humidity sensor 1008 in the shape of fingers, plates,plates with holes to allow access for the ambient humidity to theunderlying polyimide dielectric component 905.

The metallic layer may also be used in the device 1000 for the magneticsensor 1002 to form a protective layer over the cap structural component880. If the metallic layer is a magnetic layer such as Nickel, it may beused in magnetic sensor 1002 to form a reference magnet.

Another layer is used in the device 1000 in addition to the layers usedin device 500. This layer is an insulating layer used in theimplementation of the device 1000. In this exemplary implementation,this layer is a thick oxide layer deposited by PECVD.

The insulating layer is used in the infra-red sensor 1004 to protect oneof the junctions of the infrared sensor from the incident radiation. Thestructural components 910 and 911 are used to protect one of thejunctions formed between the polysilicon layer 661 and metal components906 and 907 so that the Seebeck voltage that is generated reflects theincident radiation.

The insulating layer is used in the force sensor 1006 to form a dynamicstructural component 912 that combines with the dynamic structuralcomponent 883, which is the diaphragm. The layer insulating is used toform the force concentrator or force transmitter 912 that transmits theforce being measured to the dynamic structural component 883. The forcetransmitted by 912 causes the diaphragm 883 to deflect towards thestatic or reference plate or electrode 867 effectively changing the gapand thereby the capacitance. The change in the capacitance due to theforce transmitted as compared to a reference capacitance is a measure ofthe force being applied on 912.

The insulating layer may also be used in MIMS device 1000 for themagnetic sensor 1002 over the cap structure 880 to increase themechanical strength of the cap structure.

In MIMS device 1000, it is evident that the layers used in MIMS device500 is used to implement device 1000 along with the incremental additionof layers to implement magnetic sensor 1002, infrared sensor 1004, forcesensor 1006 and humidity sensor 1008. It will be evident to thoseskilled in the art that the combination of layers from MIMS device 500and MIMS device 1000 can be used for the parallel design and fabricationof multiple sensors with static and dynamic structural components. Thus,in the embodiments of MIMS device 500 and MIMS device 1000, a MIMSdevice can be implemented with an accelerometer, pressure sensor,microphone, magnetic sensor, infrared sensor, force sensor and humiditysensor. It will be further evident to those skilled in the art thatthese embodiments are illustrative of the parallel design andfabrication of multiple sensors that substantially share layers for theimplementation of static and dynamic components for the implementationof different sensors that respond to physical, chemical and biologicalinputs.

FIG. 38 illustrates a MIMS device 1010 used in a cellphone 1020. TheMIMS 1010 device comprises an indirect interface sensor comprising anaccelerometer 1025 and a direct interface sensor comprising a microphone1030.

FIG. 39 illustrates a MIMS device 1040 used in a transportation device1050 such as a car. The MIMS device 1040 comprises an indirect interfacesensor comprising an accelerometer 1055 and a direct interface sensorcomprising a pressure sensor 1060.

FIG. 40 illustrates a MIMS device 1070 used in a wearable device 1080such as an adhesive patch attached to an arm 1100. The MIMS device 1070comprises an indirect interface sensor comprising an accelerometer 1085and a direct interface sensor comprising a pressure sensor 1090.

From these embodiments, it will be evident to those skilled in the artthat an integrated circuit can be formed with a plurality of sensorscomprising a first sensor configured to measure a first parameter wherethe first parameter is configured to be directly applied to the sensorand a second sensor configured to measure a second parameter where thesecond parameter is configured to be indirectly applied to the sensorwhere the first and second sensors are formed on a semiconductor wafer.

From these embodiments, it will be evident to those skilled in the artthat an integrated circuit can be formed having a plurality of sensorscomprising a first sensor and a second sensor where the first sensor isconfigured to directly measure a first parameter and the second sensoris configured to indirectly measure a second parameter where the firstand second sensors are formed at the same time on a semiconductorsubstrate

From these embodiments, it will be evident to those skilled in the artthat a method is described of forming an integrated circuit having aplurality of sensors comprising a step of forming a direct sensor and anindirect sensor on a semiconductor substrate using photolithographictechniques

From these embodiments, it will be further evident to those skilled inthe art that an integrated circuit can be formed comprising a firstsensor and a second sensor where the first sensor and second sensorshare a layer in common and where the layer is configured to be rigid inthe first sensor and where the layer is configured to flex in the secondsensor.

From these embodiments, it will be further evident to those skilled inthe art that an integrated circuit can be formed having a layer wherethe layer is common to a first sensor and a second sensor of theintegrated circuit where a portion of the layer in the first sensor isconfigured not to move, where a portion of the layer in the secondsensor is configured to move, and where the layer overlies asemiconductor substrate.

From these embodiments, it will be further evident to those skilled inthe art that a method is described of forming an integrated circuitcomprising the steps of forming at least a portion of a first sensor,forming at least a portion of a second sensor, depositing a layeroverlying the first sensor and the second sensor, usingphotolithographic techniques to define the layer, etching the layerwhere the layer in the first sensor is configured not to move and wherethe layer in the second sensor is configured to move.

From these embodiments, it will be evident to those skilled in the artthat an integrated circuit can be formed comprising a first sensor; anda second sensor where the first and second sensors are formed having alayer in common, where the layer seals a cavity in the first sensor,where the layer seals a cavity in the second sensor, where the cavity ofthe first sensor has a fixed volume and where a volume of the cavity ofthe second sensor is variable

From these embodiments, it will be evident to those skilled in the artan integrated circuit can be formed comprising a first sensor and asecond sensor formed overlying a semiconductor substrate, where thefirst and second sensors are formed having a layer in common, where thelayer seals a cavity in the first sensor, where the layer seals a cavityin the second sensor, where at least a portion of the layer is removed,and where the cavity of the first sensor has a fixed volume and wherethe integrated circuit is configured to receive a stimulus that changesa volume of the cavity of the second sensor.

From these embodiments, it will be evident to those skilled in the artthat an integrated circuit can be formed comprising a first sensorcomprising a first cavity in a semiconductor substrate, a second sensorcomprising a second cavity in the semiconductor substrate, a layeroverlying the first cavity and the second cavity where the layer sealsthe first cavity having a fixed volume, where the layer seals the secondcavity, where the layer is configured to receive a stimulus that changesa volume of the second cavity, and where the first sensor is one of anaccelerometer, gyroscope, humidity sensor, magnetic sensor, flow sensor,light sensor, electrical field sensor, biological sensor, or chemicalsensor

While the present invention has been described with reference toparticular embodiments, those skilled in the art will recognize thatmany changes may be made thereto without departing from the spirit andscope of the present invention. Each of these embodiments and obviousvariations thereof is contemplated as falling within the spirit andscope of the invention.

What is claimed is:
 1. A monolithically integrated multi-sensor (MIMS)having three or more sensors the MIMS comprising: a first MEMS sensorconfigured to measure a first parameter; a second MEMS sensor configuredto measure a second parameter; a third sensor configured to measure athird parameter wherein the first, second, and third parameters aredifferent, wherein the first, second, and third sensors are formed on orin a single semiconductor substrate using a monolithic semiconductorprocess, and wherein the a layer of the monolithic semiconductor processis common to the first, second, and third sensors.
 2. The MIMS of claim1 wherein the layer forms a static structural component in at least oneof the first, second, or third sensors and wherein the layer forms adynamic structural component in at least one of the first, second, orthird sensors.
 3. The MIMS of claim 2 wherein the layer is configured toform one or more pillars or one or more walls to support the staticstructural components for improved mechanical strength.
 4. The MIMS ofclaim 2 wherein the dynamic structural component is a proof mass or asuspension spring.
 5. The MIMS of claim 2 wherein the static structuralcomponent is an electrode.
 6. The MIMS of claim 1 wherein the layerforms a protective cap structure.
 7. The MIMS of claim 6 wherein theprotective cap structure can be anchored to the single semiconductorsubstrate.
 8. The MIMS of claim 1 wherein one or more openings can beformed in a field region or a sensor region of at least one of thefirst, second, or third sensors.
 9. The MIMS of claim 8 wherein the oneor more openings in the layer expose one or more sacrificial layers andwherein etchant is configured to couple to the one or more sacrificiallayers through the one or more openings to remove the one or moresacrificial layers.
 10. The MIMS of claim 9 wherein the removal of theone or more sacrificial layers is configured to release one of thefirst, second, or third sensors.
 11. The MIMS of claim 10 wherein theone or more openings in the layer are covered after the removal of theone or more sacrificial layers.
 12. The MIMS of claim 1 wherein thelayer comprises polysilicon and wherein the one or more sacrificiallayers comprises an oxide.
 13. The MIMS of claim 1 wherein the layer ofthe monolithic semiconductor process is patterned and etchedsimultaneously on the first, second, and third sensors.
 14. The MIMS ofclaim 1 further including a second layer common to the first, second,and third sensors.
 15. The MIMS of claim 1 wherein the layer is anelectrically conductive layer.
 16. The MIMS of claim 1 wherein the layeris an electrically insulating layer.
 17. The MIMS of claim 1 wherein thelayer is a sacrificial layer.
 18. The MIMS of claim 1 wherein the first,second, and third sensors are MEMS sensors.
 19. A monolithicallyintegrated multi-sensor (MIMS) having three or more sensors the MIMScomprising: a first MEMS sensor configured to measure a first parameter;a second MEMS sensor configured to measure a second parameter; a thirdsensor configured to measure a third parameter wherein the first,second, and third parameters are different, wherein the first, second,and third sensors are formed on or in a single semiconductor substrateusing a monolithic semiconductor process, wherein a layer of themonolithic semiconductor process is common to the first, second, andthird sensors, wherein the layer forms a static structural component inat least one of the first MEMS sensor and wherein the layer forms adynamic structural component in second MEMS sensor.
 20. A monolithicallyintegrated multi-sensor (MIMS) having three or more sensors the MIMScomprising: a first MEMS sensor configured to measure a first parameter;a second MEMS sensor configured to measure a second parameter; a thirdMEMS sensor configured to measure a third parameter wherein the first,second, and third parameters are different, wherein the first, second,and third sensors are formed on or in a single semiconductor substrateusing a monolithic semiconductor process, wherein the a layer of themonolithic semiconductor process is common to the first, second, andthird sensors, wherein one or more openings in the layer can be formedin a field region or a sensor region of the at least one of the first,second, or third sensors, wherein the one or more openings in the layerexpose one or more sacrificial layers and wherein etchant is configuredto couple to the one or more sacrificial layers through the one or moreopenings to remove the one or more sacrificial layers.